Antoine Proulx

Microstructured fiber splicing

We present experimental results on Microstructured Optical Fiber (MOF) splicing with a simple method relying on conventional electric-arc splicers. The results are presented in terms of fusion losses and tensile strength. An electric-arc splicing system is used to demonstrate its effectiveness in splicing MOFs together as well as splicing MOF with a single mode fiber.

Fast pulsed electric field created from the self-generated filament of a femtosecond Ti:Sapphire laser pulse in air

Abstract We present an experiment demonstrating the generation of fast pulsed electric field from a plasma column created in air as a result of the interaction of N 2 and O 2 molecules with a 220 fs laser pulse. By first measuring the distribution of N 2 + and then by measuring the net charge present at different positions in the focal region, we determined that this plasma column has an intrinsic dipole moment, which generates these pulses. The origin of this dipole moment was attributed to longitudinal separation of electrons due to ponderomotive acceleration of electrons created through multiphoton ionization of N 2 and O 2 molecules.

Polarization dependence of the propagation of intense laser pulses in air

Measuring the photo-emission from a restricted section of a filament created in air as a result of propagation of a strong Ti:Sapphire laser pulse, the dependence of the propagation on the polarization (linear and circular) of the laser was studied. The results clearly indicate the dominant roles of two processes: self-focusing due to the nonlinear refractive index in the neutral gas and defocusing in the plasma as a result of multiphoton ionization. Multiple refocusing was observed in both polarizations.

Transverse ring formation of a focused femtosecond laser pulse propagating in air

We observe the formation of ring patterns of a focused femtosecond near IR laser pulse propagating in air before the geometrical focal point. These rings are due to the combined effects of self-focusing and defocusing created by the generated plasma via multiphoton/tunnel ionization of air. Qualitative agreement is found with numerical simulations, using input conditions similar to those in the experiment.

Modeling the photodegradation of large mode area Yb-doped fiber power amplifiers

Photodarkening is presently a major concern for the long term reliability and efficiency of high power Yb-doped fiber lasers and amplifiers. This phenomenon has been associated with the formation of color centers in the fiber core of single-clad and large mode area Yb-doped fibers. However, its origin is still not well understood and to date no comprehensive model that could predict the lifetime of Yb-doped fiber-based devices has been put forward. A semi-empirical approach seems at the moment the best way to gain a better understanding of the growth behavior of photo-induced losses in Yb-doped fibers in the presence of both photodarkening and photobleaching processes. A rate equation describing the activation and deactivation of color centers involving stretched exponential functions has been developed. For this approach to be effective and reliable, a minimum of parameters is used, four to describe photodarkening and three for photobleaching. A large mode area Yb-doped fiber fabricated at INO using the MCVD process has been characterized. By properly choosing the initial pumping conditions, each parameter of the stretched exponential functions has been measured separately from the others. The model has then been used to simulate the power decay from a 1 kW, 10 ns-pulse, 100 kHz Yd-doped LMA fiber power amplifier. We show that the photodarkening behavior predicted by the model is in good agreement with the experimental results over more than 6000 hours. Such a model is general in its application but the stretched exponential parameters are unique to the type of fiber tested. The model will be a useful characterization tool for developing photodarkening-resistant fibers and for evaluating the lifetime of Yb-doped fiber-based devices affected by photodegradation.

Co-seeded Er 3+ :Yb 3+ single frequency fiber amplifier with 60 W output power and over 90% TEM 00 content

We report on the design and fabrication of an Er(3+):Yb(3+) triple clad fiber and on the power scaling of a single frequency fiber amplifier at 1.5 μm based on that fiber. In addition, we report on mode content measurements in order to reveal the overlap of the amplifier output with the TEM(00) mode. The triple clad design was used to enable high output power levels, a good slope efficiency and an excellent beam quality. A maximum single frequency output power of 61 W at 1.5 μm could be achieved with the aid of the co-seeding method, which was used to suppress parasitic processes at 1.0 μm. With a scanning ring cavity the mode content of the amplifier output was analyzed with respect to the TEM modes. For all output power levels the TEM(00) content was above 90%.

Relations between phosphorus/aluminum concentration ratio and photodarkening rate and loss in Yb-doped silica fibers

The relations between dopant concentrations (phosphorus and aluminum) and photodarkening rate, excess loss, and activation energies in ytterbium-doped silica fibers are experimentally investigated. It is shown that increasing the concentration of phosphorus from 0.2 to 2.5 mol% in phosphorus/aluminum codoped fiber cores decreases the photodarkening excess loss by a factor of 8 and the photodarkening rate by a factor of 10. Moreover, the effective number of ytterbium ions involved in the photodarkening process increases from 4 to more than 6 for tested phosphorus/aluminum concentration ratios varying from 0.1 to 1 respectively. In contrast, increasing the aluminum concentration from 2 to 5 mol% for a fixed phosphorus concentration of 0.2 mol% has negligible effect on the initial photodarkening rate or the effective number of ytterbium ions involved in the process, but still decreases the photodarkening excess loss by a factor of 5. Those results suggest photodarkening activation energies of 5.2 eV for ytterbium/aluminum-codoped silica fibers and more than 7.8 eV for ytterbium/phosphorus/aluminum-codoped silica fibers. The net improvement in photodegradation of fiber amplifiers based on such phosphorus and aluminum codoping is measured experimentally and numerically simulated. The output power loss of 1064-nm ytterbium-doped LMA fiber amplifiers with phosphorus/aluminum ratios of 0.1 and 0.6 is reduced after 10 000 hours from 17% to less than 2%, respectively. Better understanding of the effects of phosphorus and aluminum on photodarkening will help to design reliable and efficient ytterbium-doped fiber amplifiers.

Polymer Micronozzle Array for Multiple Electrosprays Produced by Templated Synthesis and Etching of Microstructured Fibers

Microstructured fibers (MSFs) having raised polymer nozzles in each channel are custom designed, fabricated, and tested for use as multiple electrospray (MES) emitters for mass spectrometry (MS). There is strong motivation to develop electrospray emitters that operate at practical flow rates but give the much greater ionization efficiency associated with lower (nano) flow rates. This can be accomplished by splitting the flow into many lower-volume electrosprays, an approach known as MES. To couple with most modern mass spectrometers, the MES emitter must have a small diameter to allow efficient ion collection into the MS. In this work, a MSF, defined as a fiber having many empty channels running along its length, was designed to have 9 channels, 9 μm each, >100 μm apart arranged in a radial pattern, all in a fiber having a compatible diameter with both front-end LC equipment and typical MS inlets. This design seeks to promote independent electrospray from each channel while maintaining electric field homogeneity. While the MSFs themselves do not support MES, the formation of polymer nozzles protruding from each channel at the tip face enables independent electrospray from each nozzle. Microscope imaging, electrospray current measurement, and ESI-MS detection of a model analyte all confirm the MES behavior of the 9-nozzle emitter, showing significant signal enhancement relative to a single-nozzle emitter at the same total flow rate. LC/MS data from a protein digest obtained at an independent laboratory demonstrates the applicability and robustness of the emitter for real scientific challenges using modern LC/MS equipment.

Improving the mode profile circularity of microstructured optical fibers by using an Archimedean-like cladding structure

We present a novel microstructured optical fiber (MOF) structure which consists of a 7-missing-holes core surrounded by a cladding formed by an Archimedean-like lattice of air holes, as opposed to the standard MOF cladding structure consisting of a triangular lattice. We demonstrate that this new cladding geometry can be achieved through the standard stack-and-draw MOF fabrication method, the main difference being the fact that the circular capillaries commonly used in conventional MOF are replaced by hexagonal canes comprising 7 air holes disposed in a centred hexagon (forming the so-called A7 unit cells). The Archimedean-like lattice MOF (ALMOF) is particularly interesting by the fact that it features a dodecagonal core, which is a shape much closer to a perfect circle than the hexagonally-shaped core characteristic of the conventional 7-missing-holes triangular-lattice MOF. As a result, we show that the improved core circularity of the ALMOF design leads to a significantly more circular fundamental mode profile, which can prove to be quite interesting for specific applications where the circularity of the mode profile is critical, such as precision laser micromachining for example.

Low-loss splicing of microstructured fibers with conventional electric-arc splicers

We present experimental results demonstrating the possibility of obtaining low-loss splices of microstructured optical fibers (MOFs) by using conventional electric-arc splicers. We show evidence of the effectiveness of the method by splicing two MOFs together as well as a MOF with a standard single mode fiber (SSMF). The results are presented in terms of fusion losses and tensile strength. Theoretical calculations of the losses attributable to mode mismatch between the MOF and the SMF suggest that the splicing losses could be further reduced by optimizing the MOF design parameters. For the case of a MOF-MOF splicing, the loss that could be due to a possible rotational misalignment that comes with the non-cylindrical symmetry of the modal distribution is also evaluated.