Mukul Chandra Paul

Wideband EDFA Based on Erbium Doped Crystalline Zirconia Yttria Alumino Silicate Fiber

A wideband erbium-doped fiber amplifier (EDFA) is demonstrated using an Erbium-doped zirconia fiber as the gain medium. With a combination of both Zr and Al, we could achieve a high erbium doping concentration of 4320 ppm in the glass host without any phase separations of rare-earths. The Erbium doped fiber (EDF) is obtained from a fiber preform, which is fabricated in a ternary glass host, zirconia-yttria-aluminum codoped silica fiber using a MCVD process. Doping of Er2O3 into Zirconia yttria-aluminosilicate based glass is done through solution doping process. The maximum gain of 21.8 dB is obtained at 1560 nm with 2 m long of EDF and co-pumped with 1480 nm laser diode. At high input signal of -4 dBm, a flat-gain at average value of 8.6 dB is obtained with a gain variation of less than 4.4 dB within the wavelength region of 1535-1605 nm and using 3 m of EDF and 100 mW pump power. The corresponding noise figure is maintained below 9.6 dB at this wavelength region.

Design of all-solid leakage channel fibers with large mode area and low bending loss

We investigate a novel design for all-solid large mode area (LMA) leakage channel fibers (LCFs) for high-power Yb-doped fiber lasers and amplifiers, based on a single down-doped-silica rod ring surrounding a seven-cell pure-silica core, aiming for effectively single-mode behavior and low bending loss characteristics. Through detailed numerical simulations based on the finite element method (FEM), we find that the proposed all-solid LMA-LCFs, having a seven-cell core and two different sizes of down-doped rods, can achieve sufficient differential mode loss and much lower bending loss, as compared with a previously-reported LCF with a one-cell core and six large down-doped-silica rods.

Performance comparison of Zr-based and Bi-based erbium-doped fiber amplifiers.

In this Letter, we present a comprehensive comparison of the performance of a zirconia-based erbium-doped fiber amplifier (Zr-EDFA) and a bismuth-based erbium-doped fiber amplifier (Bi-EDFA). The experimental results reveal that a Zr-EDFA can achieve comparable performance to the conventional Bi-EDFA for C-band and L-band operations. With a combination of both Zr and Al, we could achieve a high erbium-doping concentration of about 2800 ppm (parts per million) in the glass host without any phase separations of rare earths. The Zr-based erbium-doped fiber (Zr-EDF) was fabricated using in a ternary glass host, zirconia-yttria-aluminum codoped silica fiber through a solution-doping technique along with modified chemical vapor deposition. At a high input signal of 0 dBm, a flat gain at average value of 13 dB is obtained with a gain variation of less than 2 dB within the wavelength region of 1530-1575 nm and using 2 m of Zr-EDF and 120 mW pump power. The noise figures are less than 9.2 at this wavelength region. It was found that a Zr-EDFA can achieve even better flat-gain value and bandwidth as well as lower noise figure than the conventional Bi-EDFA.

Mass density and the Brillouin spectroscopy of aluminosilicate optical fibers

Provided herein is a detailed analysis of the Brillouin properties of alumina-doped silica optical fiber. The acoustic velocity of alumina in silica is shown to be a very strong function of its mass density, which can vary significantly from sample-to-sample and likely originates from the observed linear relationship between the longitudinal elastic modulus and the mass density. Further, the refractive index versus the alumina concentration provides a very sensitive probe of this mass density, and can be used to derive other structural details about the alumina. For example, for the first time to the best of our knowledge measurements of the thermo- and strain-acoustic coefficients (TAC and SAC, respectively) of the alumina dopant in silica-based fiber are presented and it is shown that these quantities are not strongly influenced by the density of alumina. Further, the material acoustic damping does not appear to be strongly influenced by the density. The TAC and SAC, or the dependence of the acoustic velocity on temperature or strain, respectively, are both found to be negative and large for alumina, in fact much larger than those for silica. Alumina thus represents a unique and potentially very useful material for the compositional tuning of the Brillouin scattering characteristics of optical fibers for distributed sensing and other applications. Conversely, these properties of alumina reduce the effectiveness of using applied temperature or strain gradients to fiber in order to suppress Brillouin scattering in fiber laser systems.

Thermal regenerated grating operation at temperatures up to 1400°C using new class of multimaterial glass-based photosensitive fiber

The work demonstrates for the first time a thermal regenerated grating (RG) operating at an ultra-high temperature up to 1400°C. A new class of photosensitive optical fiber based on erbium-doped yttrium stabilized zirconia-calcium-alumina-phospho silica (Er-YZCAPS) glass is fabricated using modified chemical vapor deposition (MCVD) process, followed by solution doping technique and conventional fiber drawing. A type-I seed grating inscribed in this fiber is thermal regenerated based on the conventional thermal annealing technique. The investigation result indicates that the produced RG has an ultrahigh temperature sustainability up to 1400°C. The measured temperature sensitivities are 14.1 and 15.1 pm/°C for the temperature ranges of 25°C-1000°C and 1000°C-1400°C, respectively.

The mechanism of rare earth incorporation in solution doping process

The mechanism involved during solution doping process has been systematically investigated by correlating the soot characteristics and solution parameters with the amount of rare earth (RE) incorporated in the core of optical fiber. Experiments show that the amount of RE incorporation may be controlled with better precision by adjusting Al ion concentration in the soaking solution. A model has been developed on the basis of cooperative adsorption mechanism correlating different parameters in the overall process. Theoretical estimation shows good agreement with the experimental results and can be used to predict the extent of RE incorporation for any composition if the soot layer characteristics are known.

Limitation on Effective Area of Bent Large-Mode-Area Leakage Channel Fibers

We investigate the bending characteristics of leakage channel fibers (LCFs) to achieve large mode area (LMA) and effectively single-mode operation with a practically allowable bending radius for compact Yb-doped fiber applications. Through numerical simulations, carried by the full-vectorial finite-element method, we present the limitations on the effective area of LCFs under bent condition and compare their limits with that of conventional step-index LMA fibers. Due to a better controllability of the low numerical aperture and a large value of the differential bending loss (~20 dB/m) between the fundamental and higher order modes in LCFs, the LMA of ~500 μm2 (core diameter of ~36 μm) at 1064 nm can be achieved when the optimized LCF is bent into a 10 cm bending radius.

Fabrication and application of zirconia-erbium doped fibers

In this work, the fabrication of a Zirconia-Erbium co-Doped Fiber (Zr-EDF) and its application in the generation of non-linear effects as well as use in a compact pulsed fiber laser system is described. The Zr-EDF is fabricated by the Modified Chemical Vapor Deposition (MCVD) technique in combination with solution doping to incorporate the glass modifiers and nucleating agent. The resulting preforms are annealed and drawn into fiber strands with a 125.0 ± 0.5 µm diameter. Two Zr-EDFs, ZEr-A and ZEr-B, are fabricated with erbium ion concentrations of 2800 and 3888 ppm/wt and absorption rates of 14.5 and 18.3 dB/m at 980 nm respectively. Due to its higher erbium dopant concentration, a 4 m long ZEr-B is used to demonstrate the generation of the Four-Wave-Mixing (FWM) effect in the Zr-EDF. The measured FWM power levels agree well with theoretical predictions, giving a maximum FWM power - 45 dBm between 1558 nm to 1565 nm, and the generated sidebands are as predicted. The non-linear coefficient of ZEr-B is measured to be 14 W−1km−1, with chromatic and slope dispersion values of 28.45 ps/nm.km and 3.63 ps/nm2.km respectively. The ZEr-B is also used together with a graphene based saturable absorber to create a compact, passively Q-switched fiber laser. Short pulses with a pulse width of 8.8 µs and repetition rate of 9.15 kHz are generated at a pump power of 121.8 mW, with a maximum average output power of 161.35 µW and maximum pulse energy value of 17.64 nJ. The fabricated Zr-EDF has many potential applications in multi-wavelength generation as well as in the development of compact, pulsed laser sources.

Diode-pumped 1028 nm Ytterbium-doped fiber laser with near 90% slope efficiency

Highly efficient laser action from an Ytterbium-doped fiber (YDF) is demonstrated using a fiber Bragg grating (FBG) in conjunction with a 4% Fresnel reflection at room temperature. The YDF used is drawn from Yb2O3-doped preform, fabricated through deposition of porous layer of composition SiO2-GeO2 by the MCVD process in conjunction with a solution doping technique. The fabricated YDF has a core composition of 0.2 wt % of Yb2O3, 1.8 wt % of Al2O3 and 23 wt % of GeO2 with a pump absorption of 9.0 dB/m. The fiber laser operates at wavelength of 1028 nm with a slope efficiency of 88% with respect to the launched 976 nm pump power using the YDF length of 7 m.

Design and fabrication of an intrinsically gain flattened Erbium doped fiber amplifier

We report design and subsequent fabrication of an intrinsically gain flattened Erbium doped fiber amplifier (EDFA) based on a highly asymmetrical and concentric dual-core fiber, inner core of which was only partially doped. Phase-resonant optical coupling between the two cores was so tailored through optimization of its refractive index profile parameters that the longer wavelengths within the C-band experience relatively higher amplification compared to the shorter wavelengths thereby reducing the difference in the well-known tilt in the gains between the shorter and longer wavelength regions. The fabricated EDFA exhibited a median gain ≥28 dB (gain excursion below ±2.2 dB within the C-band) when 16 simultaneous standard signal channels were launched by keeping the I/P level for each at ―20 dBm/ channel. Such EDFAs should be attractive for deployment in metro networks, where economics is a premium, because it would cut down the cost on gain flattening filter head.