Hiroaki Yanagita

Mechanisms of upconversion fluorescences in Er3+, Tm3+ codoped fluorozircoaluminate glasses

The upconversion of infrared radiation into green and red fluorescences has been investigated for Er3+ and Tm3+ codoped fluorozircoaluminate glasses under 790 nm excitation. Introduction of Tm3+ into Er3+ doped system preferentially quenches the green upconversion fluorescence from the 4S32 level of Er3+ due to the efficient cross-relaxation of 4I132 → 4I152 (Er): 3H6 → 3H4(Tm) which can significantly reduce the upconversion efficiency from the 4I132 level to the emitting 4S32 level. However, the Tm3+ behaves as a good sensitizer of the red upconversion fluorescence from the 4F92 level of Er3+ which is mainly populated by the cross-relaxation of 3H4 → 3H6 (Tm): 4I112 → 4F92(Er). The excitation energy stored in the 4I112 level of Er3+ migrates through the glass with a diffusion-limited regime. Through this regime, only Er3+ ions which have diffused their energy into the vicinity of Tm3+ ions can transfer the energy to the 3H5 level of Tm3+. At lower Er3+ concentrations (≤ 3 mol%), this diffusion-limited energy migration is not so efficient as to enable energy transfer upconversion from the 4I112 level to the 4F92 level of Er3+.

Pr3+ doped InF3/GaF3 based fluoride glass fibers and Ga–Na–S glass fibers for light amplification around 1.3 μm

Abstract We have developed three types of highly efficient Pr 3+ doped fiber (PDF) amplifiers around 1.3 μm based on non-oxide glasses. A Pr 3+ doped InF 3 /GaF 3 based fluoride glass fiber module (PFDM) has a gain coefficient: 0.29 dB/mW and a signal output power: 15.2 dBm (33 mW) at a pump power of 272 mW. A Pr 3+ doped chalcogenide system: Ga–Na–S (GNS) single-mode fiber has a larger gain coefficient: 0.81 dB/mW at signal wavelength of 1340 nm for signal input of −30 dBm. However, GNS–PDFs are best suited for amplification in the wavelength range of 1325–1350 nm when the input power is > −8 dBm. We propose a hybrid PDF consisting of the above two types of PDFs which has a flatter gain spectrum in the 1.3 μm wavelength region and will be able to extend the range of the wave division multiplexing (WDM) usage.

Transparent Conductive Cu-doped ZnSe Film Deposited at Room Temperature Using Compound Sources Followed by Laser Annealing

The evaporation of ZnSe and Cu2Se powders was used to deposit a Cu-doped ZnSe film on a glass substrate at room temperature; this was followed by laser beam (λ= 355 nm) annealing. The film consisted of a zinc blende, ZnSe, crystalline single phase with the chemical composition (Zn0.9Cu0.1)Se. Over 70% optical transmittance was obtained in the green–red region. The film had a p-type polarity with a conductivity of 0.45 S cm-1 and a workfunction of 4.7 eV. P–n diodes fabricated with the film on an n-type ZnSe:Cl layer showed rectangular behavior with a small turn-on voltage of ~1.5 V, which is plausibly explained by development of an impurity band.

Al–Zr fluoride glass for Ho 3+ –Yb 3+ green upconversion

A fluoroaluminozirconate glass was compared with a fluorozirconate and a fluoroaluminate glass as a host material for upconversion emissions in a Ho3+–Yb3+-codoped system. The green emission of 543 nm is 50% stronger in fluoroaluminozirconate than in fluorozirconate. This is because the emission is primarily governed by the Yb3+–Ho3+ energy-transfer rate rather than by the multiphonon decay rate of the emitting level. The optimum concentrations of Ho3+ and Yb3+ ions for emission intensity are 0.2 and 3.0 cationic %, respectively, at a pumping density of 560 W/mm2. By tuning a pump wavelength we also observed intense UV–blue upconversion emissions from the fluoroaluminozirconate fiber sample.

Diode-pumped Er3+ glass laser at 2.7 um

Diode-pumped cw laser oscillations in the 2.7 micrometers region were obtained using 10 mol% ErF3 doped fluorozircoaluminate glass fibers. Lasing threshold proportionately decreased with decreasing fiber core diameter. The minimum threshold observed for 110 micrometers core fiber was approximately 10 mW in absorbed pump power. Maximum slope efficiency of 8% was obtained for 1% output coupling. Output performance was significantly affected by the pump wavelength. The mechanism of cw lasing in this self-terminating system was discussed.

2.7-um diode-pumped fiber laser

The performances of diode-pumped 2.7?m fiber laser have been studied. From the population inversion estimated for a fluorozircoaluminate (AZF) glass with different ErF3 doping, a higher gain was expected for a higher ErF3 doping. The laser performances were improved by adjusting fiber length. Maximum output power of 18.5mW and slope efficiency of 7% were obtained by using 10mol% ErF3 doped, 25mm long AZF fiber in the 800nm pumping. A cw lasing was achieved by diode-pumping at 0. 98pm and the effect of Yb3+ sensitization was discussed to improve the performance.

Validation of the p-type Behavior of an Ag-doped ZnSe Film Grown Heteroepitaxially on GaAs(100) Substrate

To validate p-type semiconducting behavior in Ag-doped ZnSe, single-crystal films were grown on GaAs(100) substrates using an evaporation method with ZnSe and Ag 2 Se powder sources. The heteroepitaxial relationship between ZnSe(100) and GaAs(100) was observed using X-ray diffraction and transmission electron microscopy; secondary phases containing silver or silver selenide were not detected. A film doped with Ag at 1 10 20 atm·cm -3 had a conductivity of 1.5 x 10 -5 S·cm -1 . The hot-probe test indicated p-type polarity, with a clear and reproducible rectifying characteristic demonstrated by forming a ZnSe:Ag/p-GaAs:Zn junction. The work function of a ZnSe:Ag film measured by ultraviolet photoelectron spectroscopy was 6.3 eV. The ZnSe:Ag film is suitable as an injection layer in widegap semiconductor devices and organic light-emitting diodes.

Hybrid Pr/sup 3+/-doped fiber amplifier comprising of fluoride and chalcogenide glasses

Summary form only given. We have proposed a novel configuration of Pr/sup 3+/-doped fluoride/chalcogenide glass fibre amplifier which realizes a flat output spectrum and higher output power in the 1290-1330-nm wavelength region.