Takenobu Suzuki

Ultrabroadband supercontinuum generation from ultraviolet to 6.28 μm in a fluoride fiber

Ultrabroadband supercontinuum light expanding from ultraviolet to 6.28 μm is generated in a centimeter-long fluoride fiber pumped by a 1450 nm femtosecond laser. The spectral broadening in the fluoride fiber is caused by self-phase modulation, Raman scattering and four-wave mixing. The experimental and simulated results show that fluoride fiber is a promising candidate for generating the midinfrared supercontinuum light up to 8 μm.

Tellurite microstructure fibers with small hexagonal core for supercontinuum generation

Tellurite glass microstructure fibers with a 1 microm hexagonal core were fabricated successfully by accurately controlling the temperature field in the fiber-drawing process. The diameter ratio of holey region to core (DRHC) for the fiber can be adjusted freely in the range of 1-20 by pumping a positive pressure into the holes when drawing fiber, which provides much freedom in engineering the chromatic dispersion. With the increase of DRHC from 3.5 to 20, the zero dispersion wavelengths were shifted several hundred nanometers, the cutoff wavelength due to confinement loss was increased from 1600 nm to 3800 nm, and the nonlinear coefficient gamma was increased from 3.9 to 5.7 W(-1)/m. Efficient visible emissions due to third harmonic generation were found for fibers with a DRHC of 10 and 20 under the 1557 nm pump of a femtosecond fiber laser. One octave flattened supercontinuum spectrum was generated from fibers with a DRHC of 3.5, 10 and 20 by the 1064 nm pump of a picosecond fiber laser. To the best of our knowledge, we have for the first time fabricated a hexagonal core fiber by soft glass with such a small core size, and have demonstrated a large influence of the holey region on the dispersion, nonlinear coefficient and supercontinuum generation for such fiber.

Broadband 1400 nm emission from Ni2+ in zinc—alumino—silicate glass

Broadband near-infrared emission from Ni2+ in zinc–alumino–silicate glass was observed at room temperature. The emission band had a peak at ∼1400 nm with a bandwidth more than 300 nm, and covered the O, E, S, C, and L bands (1260–1625 nm). The emission lifetime was more than 200 μs even at room temperature. The observed near-infrared emission could be attributed to the 3A2g(3F)→3T1g(3F) transition of Ni2+ in octahedral sites. This nickel-doped glass can be expected as an amplification medium for tunable lasers and broadband optical amplifiers for the wavelength division multiplexing transmission system applications.

Microstructured chalcogenide optical fibers from As2S3 glass: towards new IR broadband sources

The aim of this paper is to present an overview of the recent achievements of our group in the fabrication and optical characterizations of As(2)S(3) microstructured optical fibers (MOFs). Firstly, we study the synthesis of high purity arsenic sulfide glasses. Then we describe the use of a versatile process using mechanical drilling for the preparation of preforms and then the drawing of MOFs including suspended core fibers. Low losses MOFs are obtained by this way, with background level of losses reaching less than 0.5 dB/m. Optical characterizations of these fibers are then reported, especially dispersion measurements. The feasibility of all-optical regeneration based on a Mamyshev regenerator is investigated, and the generation of a broadband spectrum between 1 µm and 2.6 µm by femto second pumping around 1.5 µm is presented.

Magnetic and structural properties of (CoxFe100−x)50Pt50 alloy thin films

A study of magnetic and structural properties of (CoxFe100−x)50 (0≦x≦100) alloy thin films as functions of composition and substrate deposition-temperature Ts is carried out. The intrinsic perpendicular magnetic anisotropy Ku starts to increase with deposition temperature Ts for all the films (0≦x≦100) at about TS=250–300 °C, and then becomes nearly constant. The maximum values of Ku at room temperature thus obtained are 6×107, 4×107, and 2×107 erg/cc for Fe50Pt50, (Co43Fe57)50Pt50 and Co50Pt50, respectively. Also, the Ku of Fe50Pt50 films increases with the order parameter (S), being closely related with the tetragonality c/a. These results indicate that the evolution of Ku is due to the occurrence of the ordered fct phase.

Ultrabroadband near-infrared emission from Bi-doped Li2O–Al2O3–SiO2 glass

A broad near-infrared emission of Bi-doped lithium alumino silicate glasses has been investigated. It was found that the peak wavelength and width of the emission from the glasses could be controlled drastically by the excitation wavelength. The emission spectrum had the broadest bandwidth of more than 500nm under 900nm excitation. The emission consisted of two Gaussian peaks and the stimulated emission cross sections at the peaks were calculated as 7.3×10−21 and 2.3×10−20cm2. The lifetime was almost independent of temperature up to 350K, indicating that the emission from the Bi-doped lithium alumino silicate glass has strong resistance to the thermal quenching.

Optical properties of transparent Li2O–Ga2O3–SiO2 glass-ceramics embedding Ni-doped nanocrystals

Transparent Li2O–Ga2O3–SiO2 (LGS) glass-ceramics embedding Ni:LiGa5O8 nanocrystals were fabricated. An intense emission centered around 1300nm with the width of more than 300nm was observed by 976nm photoexcitation of the glass-ceramics. The lifetime was more than 900μs at 5K and 500μs at 300K. The emission could be attributed to the T2g3(F3)→A2g3(F3) transition of Ni2+ in distorted octahedral sites in LiGa5O8. The product of stimulated emission cross section and lifetime for the emission was about 3.7×10−24cm2s and was a sufficiently practical value.

Fabrication and characterization of a chalcogenide-tellurite composite microstructure fiber with high nonlinearity

A highly nonlinear composite fiber, which has a 1.5 microm chalcogenide glass core surrounded by a tellurite glass microstructure cladding, has been fabricated by the method of stack and draw. A tellurite glass capillary containing a As(2)S(3) rod was sealed with negative pressure inside. Then this capillary and other empty capillaries were stacked into a tellurite glass tube, and elongated into a cane. This cane was then inserted into another tellurite glass jacket tube and drawn into the composite microstructure fiber. The fiber has a flattened chromatic dispersion together with a zero dispersion wavelength located in the near infrared range. The propagation losses at 1.55 microm were 18.3 dB/m. The nonlinear coefficient at 1.55 microm was 9.3 m(-1)W(-1). Such a high nonlinear coefficient counteracts the high propagation losses to a large extent. A supercontinuum spectrum of 20-dB bandwidth covering 800-2400 nm was generated by this composite microstructure fiber.

A highly non-linear tellurite microstructure fiber with multi-ring holes for supercontinuum generation

We have fabricated a highly nonlinear complex microstructure tellurite fiber with a 1.8 micron core surrounded by four rings of holes. The cane for the fiber was prepared by combining the methods of cast rod in tube and stacking. In the process of fiber-drawing a positive pressure was pumped into the holes of cane to overcome the collapse of holes and reshape the microstructure. The correlations among pump pressure, hole size, surface tension and temperature gradient were investigated. The temperature gradient at the bottom of the preforms neck region was evaluated quantitatively by an indirect method. The chromatic dispersion of this fiber was compared with that of a step-index air-clad fiber. It was found that this fiber has a much more flattened chromatic dispersion. To the best of our knowledge this is the first report about a soft glass microstructure fiber which has such a small core together with four rings of holes for the dispersion engineering. The SC generation from this fiber was investigated under the pump of a 1557 nm femtosecond fiber laser. Infrared supercontinuum generation, free of fine structure, together with visible third harmonic generation was obtained under the pump of a femtosecond fiber laser with a pulse energy of several hundred pJ.

Ultrabroadband near-infrared emission from a colorless bismuth-doped glass

The characteristics of bismuth-doped glasses were investigated as colorless ultrabroadband near-infrared gain media. The colorless Bi-doped soda-lime-silicate glass was prepared under controlled redox conditions, and it realized the broadest near-infrared emission of about 600nm in full width at half maximum, centered at 1000nm, under 720nm excitation. The emission band extended toward shorter wavelengths compared with the shortest wavelength for the Bi-doped glass ever reported. The colorless Bi-doped glass developed in this work has a good potential for the broadband gain media for amplifiers and tunable lasers.