Highly birefringent chalcogenide optical fiber for polarization-maintaining in the 3-8.5 µm mid-IR window.

A highly birefringent polarization-maintaining chalcogenide microstructured optical fiber (MOF) covering the 3-8.5 µm wavelength range has been realized for the first time. The fiber cross-section consists of 3 rings of circular air holes with 2 larger holes adjacent to the core. Birefringence properties are calculated by using the vector finite-element method and are compared to the experimental ones. The group birefringence is 1.5x10-3 and fiber losses are equal to 0.8 dB/m at 7.55 µm.

Modal decomposition technique for multimode fibers.

We propose a new solution for modal decomposition in multimode fibers, based on a spectral and spatial imaging technique. The appearance of spurious modes in the spectral and spatial processing of the images at the output of the fiber under test when it has more than two modes is demonstrated theoretically. The new method, which allows us to identify spurious modes, is more accurate, simpler, and faster than previously reported methods. For demonstration, measurements in a standard step-index multimode fiber and a small-core microstructured fiber are carried out successfully.

Generation of a broadband single-mode supercontinuum in a conventional dispersion-shifted fiber by use of a subnanosecond microchip laser.

We report the experimental generation, simply by use of a subnanosecond microchip laser at 532 nm and a conventional dispersion-shifted fiber, of a supercontinuum that spans more than 1100 nm. We show by detailed spectral analysis that this supercontinuum originates from a preliminary four-wave mixing process with multimode phase matching and subsequent double-cascade stimulated Raman scattering and is transversely single mode as a result of Raman-induced mode competition. This technique is believed to be the simplest configuration that allows one to generate a stable supercontinuum.

Polarization mode dispersion and vectorial modulational instability in air-silica microstructure fiber.

The birefringence of an air-silica microstructure fiber has been studied by measurement of the fiber polarization mode dispersion (PMD) over the wavelength range 545-640 nm. The experimental results are shown to be in good agreement with vectorial numerical calculations, assuming an elliptical core with an eccentricity of 7%. We also report controlled experiments studying nonlinear vectorial modulation instability in the fiber, yielding 3.9-THz modulational instability sideband shifts that are in good agreement with theoretical predictions based on the calculated fiber dispersion and PMD characteristics.