John M. Fini

Bend-resistant design of conventional and microstructure fibers with very large mode area.

Achieving very large mode area is a key goal in current research on microstructure and solid fibers for high power amplifiers and lasers. One particular design regime of recent interest has effective area over 1000 square microns and has effectively-single-mode operation ensured by bend losses of the higher-order modes. Simulations show that these fibers are extremely prone to bend-induced distortion and reduction in mode area. The calculated area reduction would significantly impact nonlinear impairments for bend radii relevant to any reasonable spooled package, and can be over 50 percent for bend radii tighter than 10cm. The parabolic-profile design has a natural immunity to bend-induced mode distortion and contraction, and shows superior performance in simulated fair comparisons with other fiber families, including microstructure fibers.

Design of solid and microstructure fibers for suppression of higher-order modes

Hole-assisted fibers have been proposed for a number of applications, including low-bend-loss access transmission. Suppression of higher-order modes is essential in these designs, and is explained here as the result of index-matched coupling between core and cladding modes. This physical principle is shown to explain previous empirically optimized designs, and enables intuitive generalizations. The improved tradeoff between bend loss and suppression of higher-order modes in these designs is discussed. Novel solid and microstructure fiber designs with suppressed higher-order modes illustrate these principles.

Dispersion-stabilized highly-nonlinear fiber for wideband parametric mixer synthesis

Conventional highly-nonlinear fiber (HNLF) designs are optimized for high field-confinement but are also inherently susceptible to dispersion fluctuations. The design compromise prevents fiber-optical parametric mixers from possessing high power efficiency and extended operating bandwidth simultaneously. Using a new fiber waveguide design, we have fabricated and tested a new class of HNLF that possesses a significantly lower level of dispersion fluctuations while maintaining a high level of field-confinement comparable to that in conventional HNLFs. The fiber was used to demonstrate an all-fiber parametric oscillator operating in short-wavelength infrared (SWIR) band with a watt-level pump, for the first time.

Aircore microstructure fibers with suppressed higher-order modes

A strategy for suppressing higher-order modes in aircore bandgap fibers is proposed. Simulations confirm that significant suppression of unwanted modes is achieved by including index-matched air-guiding structures in the cladding. Suppressing higher-order modes offers to improve the fundamental loss limit in aircore fibers, addressing a key obstacle to the development of this technology.

Distributed fiber filter based on index-matched coupling between core and cladding

A new type of fiber for distributed filtering is proposed, designed to have resonant coupling between core and cladding at desired wavelengths. Design principles are illustrated with simulations of several fibers. A filter fiber was fabricated following this design strategy. Measured transmission spectra and imaging of mode output confirm the expected resonant coupling between core and cladding near 1100nm.

Perturbative numerical modeling of microstructure fibers

Modeling of microstructure fibers often involves severe computational bottlenecks, in particular when a design space with many degrees of freedom must be analyzed. Perturbative versions of numerical mode-solvers can substantially reduce the computational burden of problems involving automated optimization or irregularity analysis, where perturbations arise naturally. A basic theory is presented for perturbative multipole and boundary element methods, and the speed and accuracy of the methods are demonstrated. The specific optimization results in an elliptical-hole birefringent fiber design, with substantially higher birefringence than the intuitive unoptimized design.

Suppression of stimulated Raman scattering in a cladding pumped amplifier with an Yb-doped filter fiber

A cladding-pumped, high-power amplifier was built incorporating a star-shaped, Ybdoped filter fiber. Pulsed amplifier measurements demonstrate strong suppression of stimulated Raman scattering accomplished by a special index profile with an up-doped ring.

Comment on: Quantum optics with particles of light

Errors in the recent article, Quantum optics with particles of light, are discussed. Dispersed states resulting from linear optics are simply coherent states, and have no interesting quantum statistics.