MCVD Method Research Articles

Visible silica fiber laser based on Dy:BaF2 nanoparticle doping

A silica fiber laser based on Dy3+-doped nanoparticles (NPs) and operating at a wavelength of ∼581.5 nm is reported. Specifically, Dy-doped BaF2 nanoparticles were synthesized, and suspension doped into an aluminosilicate preform fabricated using conventional MCVD methods. Though the precursor BaF2 reacts partially with the SiO2 host, a presumed barium rich environment and localized doping persists. Spectroscopic characterization included visible emission spectrum, fluorescence decay, and loss of spectrum measurements and, where applicable, comparisons are made to previously reported Dy3+-doped silica visible fiber lasers. To the best of the author’s knowledge, this is the first report on a dysprosium NP-doped silica fiber and visible fiber laser made using this approach. This work paves the way for the development of visible silica fiber lasers with engineered local environments surrounding the rare earth ions.

Heat treatment and fiber drawing effect on the matrix structure and fluorescence lifetime of Er- and Tm-doped silica optical fibers

We investigate the influence of the optical fiber fabrication process on the fluorescence lifetime of Er3+ and Tm3+ ions. Optical fiber preforms were prepared using the MCVD method combined with Al2O3 nanoparticle doping. The preforms were subjected to various fabrication processes, such as preform elongation, fiber drawing, and heat treatment. The matrix structure of the preforms and fibers was studied by XRD and TEM. The fluorescence lifetime was measured. The fabrication processes caused the dissolution of the doped Al2O3 nanoparticles and a significant decrease of fluorescence lifetime of Tm3+ ions, from 875 µs in the preform down to 610 µs in the fiber, whereas no significant effect was observed for Er3+ ions, with fluorescence lifetime in the 9.6–10.2 ms range.

Highly Er/Yb-Co-Doped Photosensitive Core Fiber for the Development of Single-Frequency Telecom Lasers

A highly erbium- and ytterbium-co-doped photosensitive fiber with a germanophosphosilicate glass core was fabricated by the MCVD method, utilizing an all-gas-phase deposition technique developed “in-house”. Due to doping with germanium oxide (GeO2), this fiber revealed high-grade photosensitivity (without hydrogen loading) to UV laser radiation at a 193 nm wavelength. The short (28 mm) Fabry–Perot laser cavity was designed by inscribing two fiber Bragg gratings (highly and partially reflective FBGs) directly in the core of the fabricated fiber sample. The stable single-frequency operation regime of the designed laser was observed. The laser emission peak was centered at 1540 nm, with a linewidth of 50 kHz. The slope efficiency of the laser was 10%, and the maximal output power reached a level of 35 mW.

Optimization of the Core Compound for Ytterbium Ultra-Short Cavity Fiber Lasers

Highly ytterbium-, aluminum- and phosphorus-co-doped silica fibers with low optical losses were fabricated by the MCVD method, utilizing an all-gas-phase deposition technique. Optical and laser properties of the active fibers with a phosphosilicate and aluminophosphosilicate glass cores doped with 1.85 mol% and 1.27 mol% Yb2O3 were thoroughly investigated. With the help of hydrogen loading, it was possible to induce highly reflective Bragg grating in both fiber samples using the standard phase-mask technique and 193 nm-UV laser irradiation. The ultra-short (less than 2 cm long) Fabry–Perot laser cavities were fabricated by inscribing two fiber Bragg gratings (highly and partially reflective FBGs) directly in the core of the fiber samples. The highest pump-to-signal conversion efficiency of 47% was demonstrated in such laser configuration using phosphosilicate fiber. The reasons for the low efficiency of aluminophosphosilicate fiber are discussed.

Heat treatment and fiber drawing effect on the luminescence properties of RE-doped optical fibers (RE = Yb, Tm, Ho).

We investigate the influence of various optical fiber fabrication processes on the fluorescence decay of RE ions commonly used in fiber lasers and amplifiers, i.e. Yb3+, Tm3+ and Ho3+. Optical fiber preforms were prepared using the MCVD method combined with Al2O3 nanoparticle doping and subjected to subsequent heat treatment processes such as preform elongation and fiber drawing. The fluorescence decay of RE ions was measured in multiple stages of optical fiber preparation: in an original preform, in an elongated preform (cane), in a standard fiber, and in an overcladded fiber. It was found that heat treatment processing of the preforms generally leads to a faster fluorescence decay, which can be explained by the diffusion of dopants and clustering of RE ions. The fiber drawing exhibited a greater effect compared to preform elongation, which was ascribed to a faster cooling rate of the process. In general, the heat treatment of RE-doped silica glass preforms leads to the decline of fluorescence decay.

The radiation resistance nature of single-mode optical fiber with an oxygen-deficient silica glass core

The radiation resistance of single-mode fluorosilicate optical fiber with oxygen deficiency in a silica glass core was investigated. Fiber has been made by MCVD method. At γ-irradiation by a dose of 0.12 MGy optical fibers have shown two processes of change of signal attenuation different in velocity both at radiation processing and after its end. The difference in attenuation of optical fiber at wavelengths of 1.31 µm and 1.55 µm can be caused by higher radiation resistance of the fiber core material in comparison with the fiber fluorosilicate cladding. Our hypothesis is that this is due to the increased oxygen content in the cladding compared to the core, which leads to more prominent destruction of the glass matrix of the cladding and change in its optical properties.

Effect of Ultra-Low Expansion Quartz Glass Layer on the Enhancement Performance of Quartz Optical Fiber

In this paper, the prefabricated rod of quartz fiber was prepared by MCVD method. A thickness of ultra-low expansion(ULE) quartz glass was deposited in the wall of quartz tube, and then quartz and its dopants were deposited. Finally, the prefabricated rod of quartz fiber preform containing doped TiO2 layer was successfully prepared by high temperature dehydroxylation treatment. The strength of quartz fiber obtained by wire drawing for the prefab rod is significantly improved. The experimental results showed that the quartz glass layer with TiO2 doped has a lower thermal expansion coefficient, the doped of TiO2 is amount 5wt%, and the doped layer thickness is 4%, the optical fiber has the best enhancement. The maximum tensile strength of the organic coating is up to 75.5N, which is higher (6.34%) than that of the commercial optical fiber (71N).

Influence of Layer Thickness in the Mcvd Method on the Composition of Fluorosilicate Glass

Influence of Layer Thickness in the Mcvd Method on the Composition of Fluorosilicate Glass

Photosensitive Yb-Doped Germanophosphosilicate Artificial Rayleigh Fibers as a Base of Random Lasers

Asingle-mode Yb-doped germanophosphosilicate fiber with ultra-low optical losses (less than 2 dB/km) was fabricated by means of the MCVD method utilizing an all-gas-phase deposition technique developed “in house”. The absorption and luminescent spectral properties of the fiber were thoroughly studied. The photosensitivity of the pristine (non-hydrogenated) fiber to 248 nm-laser radiation was confirmed by means of fiber Bragg grating (FBG) inscription directly during the drawing process. The random single-frequency lasing at the 1060-nm-wavelength obtained in the 21-m-long fiber with an array of weak FBG was reported. The developed laser slope efficiency in the backward-pumping scheme was measured as high as 32%.

MCVD method for manufacturing polarization-maintaining and radiation resistant optical fiber with germanosilicate elliptical core

The aim of this work was to develop a fabrication process of single-mode polarization-maintaining germanosilicate optical fibers with elliptical core (GOFEC) doped with 20 mol % GeO2. The fiber preform was fabricated by MCVD method. The low-oxygen central piece of the core in the preform was removed by high-temperature chemical gas-phase etching. The influence of γ-radiation with a dose rate of 1 Gy/s on the optical losses in GOFEC at a wavelength of 1550 nm and at 25°C and −60°C were investigated. Their radiation resistance at −60°C is proved to surpass that of the existing analogous fibers. It has been found that the radiation-induced attenuation in such highly doped GeO2 single-mode fibers is higher than that in multimode fibers. In contrast to multimode fibers, radiation resistance in single-mode fibers depends on the material of the core and cladding. As to the radiation resistance, these GOFEC are comparable with the fiber of PANDA type with a pure silica glass core.

Photosensitive highly Er/Yb co-doped phosphosilicate optical fibers for continuous-wave single-frequency fiber laser applications

Highly Er/Yb co-doped phosphosilicate fibers with low optical losses were fabricated by the MCVD method, utilizing an all-gas-phase deposition technique developed “in house.” Important characteristics such as photodarkening and photosensitivity of these fibers were thoroughly investigated. An almost negligible impact of photodarkening-induced losses (no more than 1 dB/m) was discovered in the near-infrared spectral region. The photosensitivity of hydrogen-loaded fiber samples was studied using excimer laser irradiation at a wavelength of 193 nm. A photoinduced refractive index value of 1 × 10 − 3 at the total UV irradiation exposure dose of 550 J / c m 2 was achieved. A single-frequency laser with a Fabry–Perot short cavity was designed by inscribing highly reflective ( R > --> 99.9 % ) and partially reflective ( R = 94.3 % ) fiber Bragg gratings directly in the Er/Yb co-doped phosphosilicate fiber core. The laser showed stable CW output emitting with a narrow peak centered at 1551.5 nm in the absence of any signs of Y b 3 + parasite lasing in a wavelength range from 1000 to 1100 nm.

Preparation and properties of Tm-doped SiO2-ZrO2 phase separated optical fibers for use in fiber lasers

Zirconium oxide (ZrO2) is a perspective co-dopant of rare-earth ions in silica fibers for use in fiber lasers. ZrO2 nanoparticles increase the solubility of rare-earth ions and enhance their luminescence properties. In this paper, we report on the fabrication of Zr-Tm codoped silica fibers using the MCVD method combined with modified solution-doping technique. Several fibers with different dopant concentrations were prepared and their optical properties were studied. It was found that increasing Zr concentration leads to the creation of larger ZrO2 nanoparticles which causes unwanted attenuation. Optimal Zr concentration was found to be 1 at. %. The fiber with optimal Zr concentration and Tm concentration of 260 ppm exhibited 1.8 µm fluorescence lifetime of 420 ± 10 µs. For the first time in literature, we have demonstrated laser operation in a Zr/Tm-codoped silica fiber. The threshold for laser operation was determined to be 233 mW and the slope efficiency of 72.7% was achieved. MCVD combined with modified solution doping proved to be a feasible method of preparation of Tm-doped SiO2-ZrO2 optical fibers for use in fiber lasers.

Technological aspects of manufacturing silica optical fibers with large central defect of graded refractive index profile for fiber optic sensors based on few-mode effects

The paper deals with results of the study on the main technological aspects relating to a full production cycle of silica multimode graded-index fibers with the refractive index profile having central defect in the form of a large dip. Preform synthesis conditions for implementation of the mentioned defect via MCVD method have been analyzed and optimized. We have carried out research of the effect of geometrical irregularities, induced by drawing optical fibers under the manual control of the outer diameter stability, on attenuation coefficient of the graded-index 50/125 μm optical fibers with a large dip in the center of the refractive index profile. It is shown that variations of the outer diameter within the limits ± 3.5 μm lead to an increase of attenuation by 2–5 dB/km at the wavelength λ = 1310 μm as compared to the optical fibers fabricated under the automatic maintenance of the outer diameter stability. It has been determined that in the latter case fibers with the parabolic refractive index profile, corresponding to numerical aperture of 0.20, and the dip depth equal to 0.0115 demonstrate the attenuation about 5 dB/km in the second and third optical fiber transmission windows. Applying the Weibull distribution, a statistical evaluation of mechanical properties of the optical fibers drawn at various temperatures has been carried out. Based upon measurements, tensile strength of the fibers was estimated to be 5.07–5.49 GPa, that is comparable with the strength properties of silica telecom fibers. The manufactured multimode fibers are attractive candidates for developing sensing elements of registering external influences in systems of fiber-optic sensor networks based on few-mode effects.

The investigation of physicochemical processes of silica glass doping with fluorine by the MCVD method

The temperature-time dependences for sintering and fluorination processes of SiO2 nanoparticles obtained by the method of chemical vapor deposition are presented. It has been revealed that at the SiF4 pressure of 1 atm, the intensive agglomeration of high-dispersive layers prevents the achievement of equilibrium between the fluorine-containing gas media and the condensed phase. The saturation of the porous layers with fluorine occurs at temperatures less than 1100°C, when the sintering duration of high-dispersive particles is substantially longer than the fluorination process time.

Development and study of Bragg fibres with a large mode field and low optical losses

A silica Bragg fibre with optical losses lower than 10 dB km-1 is fabricated for the first time. The Bragg fibre manufactured by the MCVD method is intended for operation at a wavelength of 1.06 μm and has the mode-spot diameter 18.5 μm (the mode-spot area is 270 μm2). The fibre is considerably less sensitive to bending than step-index fibres and microstructure fibres with the same mode-spot size. The possibility of fabricating a Bragg fibre with the record mode-spot area (530 μm2 at the operating wavelength of 855 nm) for all-silica fibres is demonstrated.

Silica-based optical fibres with refractive index profiles tailored in a region of 1.46–1.62 for fibre-optic chemical detection

The paper deals with special optical fibres suitable for evanescent-wave sensing. Novel kinds of polymer-clad glass (PCG) fibres are proposed to overcome the limitation imposed by the refractive index of pure silica core of the conventional polymer-clad silica (PCS) fibres that makes impossible their use for the detection of a number of analytes with refractive indices above 1.457 (at 630 nm). The first structure proposed is the step-index (SI) one drawn from rods of soft silicate glasses with refractive index higher than that of silica. As an alternative to this kind of fibres, novel structures including inverted graded-index (IGI) and SI fibres based on doped silica with refractive indices above 1.457 and tailored by the MCVD method were devised. It was found that the sensitivity of the SI structures with the refractive index higher than 1.457 to refractive index changes was comparable to that of conventional PCS fibres. The prepared special optical fibres could be employed for evanescent-wave chemical sensing of analytes with refractive indices in a wide range, up to 1.62.

Strong photosensitivity of antimony oxide doped fibers under irradiation at 193nm

Abstract Single-mode Sb-doped fibers with ∼1.0 mol.% Sb2O5 in the core have been fabricated by the MCVD method. Photosensitivity of pristine, pre-exposed, and H2-loaded Sb-doped fibers under exposure at 193 nm has been measured and compared for the first time. Strong photosensitivity in pristine Sb-fibers has been discovered. The pre-exposure phenomenon has been found in Sb-doped fibers. However, it is weaker than in Ge and P-doped fibers. Growth of induced index and induced losses in Sb-fibers can be explained by a two-step photochemical reaction occurring in the fiber core. Modification of some different defects is proposed to occur in H2-loaded Sb-doped fiber under exposure.

On the structure of phosphosilicate glasses

Vibrational spectra of phosphosilicate glasses with P 2O 5 concentrations up to 15 mol% are investigated by the methods of Raman spectroscopy and quantum-chemical modeling. We have found that the Raman band at 1320 cm −1 characteristic for such glasses is not simple and may be decomposed into two components with frequencies at ≈1317 and ≈1330 cm −1 caused in our opinion by single phosphorus centers (OPO 3 tetrahedra surrounded by SiO 4 ones) and by double phosphorus centers (pairs of OPO 3 tetrahedra bonded by a common oxygen atom). In the investigated phosphosilicate glasses manufactured by MCVD and SPCVD methods the ratio of concentrations of single and double centers varies from 1:5 to 1:2. A novel interpretation of the Raman bands distinct from the traditional one is suggested. The approach to the Raman spectra analysis developed in this article can be applied for control and optimization of manufacturing process of phosphosilicate and similar glasses as well as optical fibers.

Peculiarities of the photosensitivity of low-loss phosphosilica fibres

The peculiarities of the refractive-index change in low-loss heavily P2O5-doped silica fibres fabricated by the MCVD method caused by irradiation with UV light are studied. The pre-exposure effect is found in these fibres. The mechanisms of the refractive-index change in phosphosilica and germanosilica fibres are considered and compared in the presence of this effect.

Spectroscopic Features of Silica Glasses Doped with Tin

The absorption, photoluminescence, and photoluminescence excitation spectra are investigated for tin-doped silica glasses synthesized by different methods. In all the glasses studied, two new centers belonging to the tin dopant in the SiO2 network are revealed in addition to the well-known oxygen-deficient center with the absorption band at 4.9 eV. One new center is associated with the absorption band at 5.9 eV and the photoluminescence bands at 2.7 and 3.6 eV, whereas the other center is characterized by the absorption band in the range of 4.56 eV and the photoluminescence band at 2.95 eV. Both new centers are identified as oxygen-deficient centers. The latter center is an analog of the centers observed in pure silica glasses synthesized in a nitrogen atmosphere and in germanosilicate glasses prepared by the MCVD and SPCVD methods. It is revealed that the formation of the oxygen-deficient center is one of the main channels of incorporating tin into the SiO2 network in all tin-containing silica glasses. Consideration is given to the reasons for the lower efficiency of the photodecay of oxygen-deficient centers in the SiO2 network in tin-containing glasses as compared to that in germanosilicate glasses and for the relatively high efficiency in the formation of the photoinduced refractive index in optical fibers with a core consisting of tin-containing silica glass.