Stefan Heinz Spalter

Large Kerr effect in bulk Se-based chalcogenide glasses

High-speed optical communication requires ultrafast all-optical processing and switching capabilities. The Kerr nonlinearity, an ultrafast optical nonlinearity, is often used as the basic switching mechanism. A practical, small device that can be switched with ~1-pJ energies requires a large Kerr effect with minimal losses (both linear and nonlinear). We have investigated theoretically and experimentally a number of Se-based chalcogenide glasses. We have found a number of compounds with a Kerr nonlinearity hundreds of times larger than silica, making them excellent candidates for ultrafast all-optical devices.

Grating resonances in air-silica microstructured optical fibers.

We report what is believed to be the first demonstration of optical fiber gratings written in photonic crystal fibers. The fiber consists of a germanium-doped photosensitive core surrounded by a hexagonal periodic air-hole lattice in a silica matrix. The spectra of these gratings allow for a detailed characterization of the fiber. In particular, the gratings facilitate coupling to higher-order leaky modes. We show that the spatial distribution and the effective index of these modes are determined largely by the design of the lattice and that the grating spectra are unaffected by the refractive index surrounding the fiber. We describe these measurements and corresponding simulations and discuss their implications for the understanding of such air-hole structures.

Strong self-phase modulation in planar chalcogenide glass waveguides

Single-mode planar waveguides were fabricated from chalcogenide glass compounds with large Kerr nonlinearities. Strong self-phase modulation of subpicosecond pulses along with low linear and nonlinear absorption losses demonstrates the potential for ultrafast, low-power, all-optical processing applications.

Bragg-grating-enhanced polarization instabilities.

Experiments demonstrate a dramatic decrease in polarization-instability threshold as an optical pulse is tuned near the short-wavelength edge of the photonic bandgap formed by a fiber Bragg grating. These enhanced nonlinear interactions and birefringent effects are modeled with coupled-mode numerical simulations. Nonlinearities are shown to increase much more rapidly than the effective birefringence as the pulse wavelength approaches the bandgap edge.

Bragg grating enhanced nonlinear polarization mode conversion

We demonstrate strong polarization mode conversion (1,2) for optical pulses with wavelengths near the edge of the photonic bandgap formed by a fiber grating.

Bragg soliton polarization evolution

Nonlinear propagation of optical pulses in fiber Bragg gratings is studied experimentally and with numerical simulations of the coupled mode equations. After a review of enhanced nonlinear interactions for pulse wavelengths near the short wavelength edge of the photonic bandgap associated with the grating, this study explores polarization evolution during nonlinear pulse propagation. Initial results for polarization instabilities and expectations for vector Bragg solitons are described.