Debjit Dutta

Chromium doped nano-phase separated Yttria-Alumina-Silica glass based optical fiber preform: fabrication and characterization

Transition metal (TM) doping in silica core optical fiber is one of the research area which has been studied for long time and Chromium (Cr) doping specially attracts a lot of research interest due to their broad emission band covering U, C and L band with many potential application such as saturable absorber or broadband amplifier etc. This paper present fabrication of Cr doped nano-phase separated silica fiber within yttria-alumina-silica core glass through conventional Modified Chemical Vapor Deposition (MCVD) process coupled with solution doping technique along with different material and optical characterization. For the first time scanning electron microscope (SEM) / energy dispersive X-ray (EDX) analysis of porous soot sample and final preform has been utilized to investigate incorporation mechanism of Crions with special emphasis on Cr-species evaporation at different stages of fabrication. We also report that optimized annealing condition of our fabricated preform exhibited enhanced fluorescence emission and a broad band within 550- 800 nm wavelength region under pumping at 532 nm wavelength due to nano-phase restructuration.

Hafnia-yttria-alumina-silica based optical fibers with diminished mid-IR (>2 µm) loss

Fabrication details and basic characteristics of a set of novel multimode hafnia-yttria-alumina-silicate (HYAS) core-glass based fibers, one of which is co-doped with bismuth (Bi), for the mid-IR (> 2 µm) spectral range are reported. It is demonstrated that fibers of this type possess low fundamental loss in the spectral range beyond 2 µm, lowered by fewer times as compared to conventional silica-based ones, even at moderate (units of mol.%) co-doping with hafnium. This makes them attractive for versatile mid-IR applications. Furthermore, HYAS core-glass fiber co-doped with Bi is revealed to have all the signs of ‘active’ (fluorescing) Bi-related centers, thus being suitable for lasing/amplifying in the near-IR spectral range.

Fabrication of ultra-high numerical aperture GeO_2-doped fiber and its use for broadband supercontinuum generation

We report the fabrication, characterization, and application (broadband supercontinuum [SC] generation) of ultra-high numerical-aperture heavily (50 mol. %) GeO2-doped optical fiber, obtained through a modified chemical vapor deposition process and rod-in-tube method. The formation of Ge-related diamagnetic defect centers, such as germanium oxygen defect centers (GeODC) with nonbridging lone electron pairs, confirmed by x-ray photoelectron spectroscopy and optical absorption studies, inducing hypolarizable local dipoles, may be responsible in boosting the nonlinear effects and enhancing stimulated Raman scattering at pumping with high-power pulses, culminating in generation of broadband SC generation. The SC spans toward the Stokes side up to 2.4 μm, under the action of ns-range pulses launched from a smartly Q-switched erbium-doped fiber laser with operation wavelength (1.56 μm) matching the zero-dispersion wavelength of the high GeO2-doped fiber.

A Flat-Gain Double-Pass Amplifier with New Hafnia-Bismuth-Erbium Codoped Fiber

An efficient and compact double-pass optical fiber amplifier is demonstrated using a newly developed hafnia bismuth erbium co-doped fiber (HBEDF) as a gain medium. The HBEDF is fabricated using a modified chemical vapor deposition in conjunction with solution doping. The fiber has an erbium ion concentration of 12500ppm. At the optimum length of 0.5m, the HBEDF amplifier (HBEDFA) achieves a Sat gain of 26dB with a gain variation of less than 1.5 dB within a wavelength region from 1530 to 1560 nm when the input signal and pump power are fixed at -30 dBm and 140mW, respectively. On the other hand, at the input signal power of -10 dBm, the HBEDFA also achieves a Bat gain of 14.2 dB with a gain variation of less than 2.5 dB within a wide wavelength region from 1525 to 1570nm. Compared with the conventional zirconia erbium co-doped fiber based amplifier, the proposed HBEDFA obtains a more efficient gain and lower noise figure. For an input signal of -30 dBm, the gain improvements of 6.2 dB and 4.8 dB are obtained at 1525nm and 1540nm, respectively.

Effects of electron-irradiation darkening and its posterior bleaching by light in novel Cr-Mg-YAS fiber

Two remarkable effects for the recently invented chromium–magnesium (Cr–Mg) co-doped yttria-alumino-silicate fiber are reported: (i) strong and spectrally peculiar darkening under the action of energetic (6 MeV) β-electrons with dosage up to 1.0 × 1015 cm−2 and (ii) posterior optical bleaching of the darkening loss at exposure to low-power (of a mW-range) 633 nm light. Both phenomena are revealed to be conspecific to co-doping the fiber with Mg and to the presence of versatile valence forms of Cr ions. The reported results seem to be impactful for exploiting fiber of such type for dosimetry and in space technology.