Cheng-Nan Tsai

400-nm-Bandwidth Emission From a Cr-Doped Glass Fiber

Cr4+-doped glass fiber by a laser-heated pedestal growth method is reported. By analyzing the absorption spectra, the transitions of Cr3+ and Cr4+ in the fibers are identified. With appropriate pumping wavelength and divalent doping concentration, both Cr3+ and Cr4+ emission bands can be excited simultaneously, and become comparable in their fluorescent intensities. As a result, more than 400-nm-width emission peaked at 1144 nm was generated at room temperature. As much as 12muW of amplified spontaneous emission was obtained by pumping with a 900-nm Ti : sapphire laser

Composition dependence of the microspectroscopy of Cr ions in double-clad Cr:YAG crystal fiber

We have demonstrated the use of microspectroscopy for measuring the Cr3+ and Cr4+ fluorescence spectra in double-clad Cr:YAG crystal fiber. The emission spectra of Cr3+ and Cr4+ are detected from core and inner cladding. The Cr3+ spectrum in the inner cladding shows a broad-band emission from 650to950nm, while the emission of Cr4+ occurs in the range of 1.15–1.55μm with a peak around 1.22μm. The characteristic of Cr ion at high-field sites shows a narrow-band emission (E2→A24 for Cr3+; E1→A23 for Cr4+), whereas that at low-field sites shows a broad-band emission (T24→A24 for Cr3+; T23→A23 for Cr4+). The emission intensity ratio of high-field sites to low-field sites in the inner cladding with different compositions has been investigated. It varies from 20% to 29% for Cr3+ and from 7.1% to 11.3% for Cr4+ when the concentration of SiO2 increases from 26.9to43.0wt%.

Enhancement of Cr4+ Concentration in Y3Al5O12 Crystal Fiber by Pregrowth Perimeter Deposition

Chromium ions tend to diffuse outward during the laser-heated pedestal growth (LHPG) of Y3Al5O12 (YAG) crystal fiber, in which the average Cr4+ ion concentration decreases significantly after each diameter-reduction step. The Cr4+ ions are replenished using an electron gun to deposit Cr2O3 and divalent-ion oxide (CaO or MgO) on the source rod circumference before LHPG. It was observed that Ca2+ has better efficiency to diffuse into the source rod more efficiently than Mg2+ generating fewer defects and stacking faults. By CaO deposition and post growth annealing at 1350 °C under an oxygen environment, a 110% increase in Cr4+ concentration was obtained. The achieved Cr4+ concentration and the ratio of Cr4+ to total Cr were 1.76×1018 cm-3 and 5.5, respectively. The Ca,Cr:YAG crystal fiber can thus be used as an ultra broadband laser material and amplified spontaneous emitter.

Crystal fiber based white light source using Ce,Sm:YAG as the active medium

White light source using double-clad Ce,Sm:YAG crystal fiber was fabricated for the first time. The color-rendering index and color temperature are estimated to be 75 and 4610 K, respectively.

Study of the side deposition enhanced Cr 4+ concentration in Cr 4+ : YAG crystal fiber as an ultra broadband amplified spontaneous emitter

Using laser heated pedestal method to grow CaO or MgO side deposited Cr4+:YAG crystal fiber, Cr4+ concentration was raised by a factor of 110% after re-growth and annealing at 1350degC in Ca,Cr:YAG crystal fiber.

Characterization on broadband chromium-doped fiber amplifier

Up to 16-dB of gross gain at a wavelength of 1.47 /spl mu/m was achieved by a broadband Cr/sup 4+/:YAG fiber amplifier. The simulation indicates that the minimum noise figure is close to 3-dB at 1.24-1.6 /spl mu/m range.

Effects of side deposition and annealing for increasing Cr 4+ concentration in Cr:YAG crystal fiber

Using electron gun to deposit CaO on the circumference of Cr:YAG crystal fiber and re-growth by laser heated pedestal growth method, the absorption coefficient of Cr4+can be achieved to 8.3 cm-1, which is equivalent to a concentration of 0.015 mol.%; while the total Cr concentration is 0.28 mol.%.