The advantage of optical fiber grating sensors are easily implemented multiplexing by using broadband light source.
Erbium doped fiber (EDF) are important as a gain media, because it affects the performance of light sources. We
demonstrated tunable fiber ring laser using Bi2O3-based Erbium doped fiber (BIEDF) and a tunable filter with bandwidth
of 1 nm. We show the BIEDF fiber length dependence, pump power dependence and also show the its spectra. By
increasing fiber lengths of BIEDF, the tunable range changes toward longer wavelengths with varying tunable range. By
using 0.7 m of BIEDF as a gain media, the tunable range reached over 110 nm with just pump power of 100 mW at 1480
nm. Tunable range was insensitive to pump power in this experiment. Also we show the laser spectra. BIEDF laser
shows high optical signal-to-noise ratio (OSNR) higher than 55 dB at over 110 nm tunable range, and 70 dB for 99 nm
(1530 - 1629 nm) tunable range. This means that BIEDF has potential for broad band fiber sensor sources, especially for
fiber grating sensors.
We have developed novel bismuth-based photonic crystal fiber which exhibits high nonlinearity γ ~ 780W-1km-1
and relatively low group-velocity-dispersion D ~ -25 ps/nm/km at 1560 nm. The new fabrication process was
also developed for this novel photonic crystal fiber with 6-fold symmetric structure. The core diameter 2.7 μm
of this fiber was designed to have modelately decreased normal dispersion and high nonlinearity. Spectral broadening
induced by self-phase-modulation by 1550 nm fs-pulse propagation shows that the high nonlinearity and dispersion reduction is simultaneously achieved.
In extreme ultraviolet (EUV) lithography technology, ultra low thermal expansion material is required as photomask substrate. We have previously developed Ti-doped silica glass which exhibits both ultra low coefficient of thermal expansion (CTE) and high homogeneity for EUV substrate. On the other hand, we have been investigating other candidate materials which have low CTE, from the viewpoint of structural chemistry. Silica glass is well-known as a low thermal expansion material and the reason is explained that in the open structure of silica glass two factors, expansion and shrinkage, compete with each other with increase in temperature. The network of silica glass consists of tetrahedra like quartz crystal. In this structure, Si is stably present with a valence of 4 and a coordination number of 4. We have carried out an atomistic simulation and estimated the volume change of oxide materials which may have the same structural transformation mechanism as SiO2. As a result, the volume of SnO2 with quartz structure (quartz-SnO2), in which Sn was present with a valance of 4 and a coordination number of 4, decreased with increase in temperature, that is, the density of quartz-SnO2 increased. Thus, it was indicated that the glass with lower CTE than that of silica glass could be obtained with substituting Sn for Si. Based on this hypothesis, we have prepared Sn-doped silica glass by Asahi silica glass producing method. The synthesized Sn-doped silica glass exhibited lower CTE than that of an ordinary silica glass.
Temperature dependences of optical path length (dS/dT; calculated using the equation, dS/dT = dn/dT + na, where a is coefficient of thermal expansion, n is refractive index and dn/dT is temperature coefficient of refractive index) in various oxide glasses were investigated. The dS/dT is generally difficult to adjust by change of glass composition because dn/dT and a are interrelated. However, low dS/dT materials are desired for optical applications such as athermal devices, and high dS/dT materials can be used for thermo-optic devices. Pure silica glass is well-known as a typical low dS/dT material but still not sufficient. Fluorine-doped silica glass showed a lower dS/dT than that of pure silica glass. By fluorine-doping in silica glass, refractive index and dn/dT decreased but a near room temperature stayed at the same level. As a result, the dS/dT decreased with increasing fluorine concentration. On the other hand, bismuthate glass showed the highest dS/dT in this study. Most glasses having high a such as tellurite glass showed negative dn/dT. However, bismuthate glasses showed positive dn/dT in spite of high a. As a result, bismuthate glasses showed quite high dS/dT. These results indicate that dS/dT of the glass can be controllable and that fluorine doped silica glass and bismuthate glass are appropriate candidate materials for optical applications.
Bismuth based erbium doped fiber and planar waveguide exhibit inherent features which cannot be realized with silica based fibers and waveguides. Extend L-band amplification, high gain C+L band amplification for coarse WDM and short pulse amplification without spectral broadening can be realized using bismuth oxide based EDF and 1-cm2-size Er doped spiral waveguide which shows >15 dB gain can be realized using bismuth oxide glass.
Bismuth based erbium doped fiber and highly nonlinear fiber exhibit inherent features which cannot be realized with silica based fibers. Extend L-band amplification, high gain C+L band amplification for coarse WDM and short pulse amplification can be realized using bismuth based EDF. On the other hand, step-index type fiber using bismuth based glass whose refractive index of 2.22 at 1.55μm is fabricated. This fiber exhibits high nonlinearity (γ=1360 W-1km-1) because of the high nonlinearity of the glass material and the small effective core area.
This paper reports on the preparation and the characteristics of Er-doped muliticomponent bismuthate channel waveguide. Dependence of emission lifetime of Er3+ ions on concentration of Er3+ ions is investigated. The concentration of Er3+ in the core film where concentration quenching effect starts is one order of magnitude higher than that of silicate materials. We show that the lower the hydroxyl ion content is, the longer the emission lifetime becomes and the emission lifetime of dehydrated core is the same as that of the fiber perform, namely the same quantum efficiency. The loss of the fabricated channel waveguide measured by cut-back method is 0.15 dB/cm at 1310 nm. Net gain of 8 dB is obtained at 1530 nm by using a 6-cm long waveguide pumped at 980 nm.
Recent developments of Bismuth-based erbium-doped fibers (Bi-EDFs) have demonstrated their potential applications for broadband amplifiers, particularly for the L-band in DWDM systems, for short pulse amplifiers to be used in very high bit-rate transmission systems (up to 160 Gbps), and for ultra wideband tunable fiber ring lasers. The low concentration quenching of erbium ions in Bi-based glass permits efficient high erbium concentration Bi-EDFs (up to 26,000 ppm) to be fabricated allowing the realization of ultra-short length erbium-doped fibre amplifiers and fiber lasers. In this paper, we reported the performance of two Bi-EDFs with different erbium ions concentrations for signal amplification. One fiber was doped with 6,470 wt-ppm of erbium ions and the other was doped with 3,250 wt-ppm of erbium ions. The performance of a 253-cm long Lanthanum co-doped Bi-based EDF (3,250 ppm of erbium) for the amplification of 142 wavelength channels was evaluated. 140 of the input signals were located at the 50-GHz ITU grid. Signal gains of over 20 dB and NF less than 6.7 dB were measured for all the channels with wavelengths ranging from 1554.13 nm to 1612.22 nm (i.e. over 58 nm). 3-dB bandwidth of 53.9 nm and quantum conversion efficiency of about 60 % were attained when the fiber was pumped with 350 mW and 623 mW of pump power, respectively. The performance of an ultra-short length Bi-EDFA, using 23-cm of Bi-EDF doped with 6,500 ppm of erbium ions pumped at 980 nm, for the amplification of picosecond pulses will be discussed. The results of an ultra wideband (106 nm) tunable fiber ring laser based on the higher erbium concentration Bi-EDF will also be presented.
Bismuth oxide based highly nonlinear fiber (Bi-NLF) enabled by glass composition and small core fiber design was successfully fabricated. There's much expectation for the development of high nonlinearity optical devices along with the large volumetric and speed increase of the information traffic in recent years. In order to achieve higher nonlinearity, it is necessary to enlarge the nonlinear refractive index n2 and make the effective core area Aeff smaller, as g is γ=2πn2/(λAeff). Much effort has been put into the development of small-Aeff holey fiber, as its high nonlinearity and dispersion can be controlled to a certain extent. However, holey fiber has issues such as large propagation loss, high connection loss with silica single-mode-fiber (SMF) because of their particular structure, and higher fabrication cost. We performed the fabrication of a conventional step-index-type SMF with high nonlinearity and low propagation loss using Bi2O3-based glass. First, we fabricated Bi2O3-based glass with high refractive index of >2.2 at 1550 nm by a conventional melting method. This glass exhibited extreme thermal stability for fiber drawing. Then in order to make Aeff smaller, cladding glass composition was designed so that the difference with the refractive index of the core glass must be large. Finally the core diameter was controlled to satisfy the single mode condition, and fiber drawing was performed. Typical Aeff of this fiber is less than 5 um2. The nonlinearity g of the fiber can be estimated to be >600 W-1km-1, as large as the value reported in holey fibers using non-silica glass. Bi-NLF with step-index-type structure would become the best candidate for short length and highly nonlinear optical devices.
Bi2O3-based thulium (Tm3+) doped glass fiber (Bi-TDF) for S-band amplification was investigated. Tm3+ was doped in Bi2O3-SiO2 based glass and melted using a conventional method. Emission spectra of the 3H4 - 3F4 were measured with pumping at a wavelength of 792 nm using laser diode (LD). Full width of half maximum (FWHM) of the emission is 1.4 times and 1.1 times broader than that of fluoride glass and tellurite glass, respectively. Moreover, the emission peak shifted towards longer wavelength as compared with fluoride and tellurite glasses. Single mode Bi-TDFs with Tm3+ concentrations of 2000 ppm, 3900 ppm and 6000 ppm were fabricated and evaluated with fusion splicing to SiO2 fibers. Gain profiles were measured with bi-directional pumping using 1047 nm Yb fiber lasers. The gain-peaks observed around 1470 nm shifted towards longer wavelength with increasing Tm3+ concentration. Gain properties of Bi-TDF were improved by additional pumping at the wavelength of 1560 nm with Tm3+ concentrations of 2000 ppm and 3900 ppm. A maximum gain over 10 dB of Bi-TDF was obtained using a fusion spliceable Bi-TDF with a length of only 100 cm.
Nonresonant-type Bi2O3-B2O3-SiO2 glass containing high concentration of Bi2O3 was prepared by a melting method. Optical Kerr shutter switching and degenerated four wave mixing experiments for this glass were performed using femtosecond laser. This glass exhibited ultrafast response below 150 femtosecond in optical Kerr switching operation. Moreover, THz optical switching was successfully performed with this glass using 1.5 THz pulse train as the gate beam. Ultrafast response and high threshold for optical damage were also confirmed with this glass at the communication wavelength of 1.5 micrometers . These results indicate that high speed switching beyond THz can be realized using Bi2O3-glass.
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