Effective area measurement of few-mode fiber using far field scan technique with Hankel transform generalized for circularly-asymmetric mode.

We report on a measurement method for the effective area of the few-mode fiber. We derived a transform equation between a near-field pattern and a far-field pattern generalized for circularly-asymmetric higher-order modes of a cylindrical core, and enabled effective area measurement of the higher-order modes using high-dynamic-range far-field scan technique and low-crosstalk mode multiplexer. The measured effective area values agreed well with the values that were numerically predicted using a finite-element method from the refractive index profile, when the modal crosstalk was suppressed.

Nanoscale Phase-Separated Structure in Core-Shell Nanoparticles of SiO-SiGeO Glass Revealed by Electron Microscopy.

SiO-based optical fibers are indispensable components of modern information communication technologies. It has recently become increasingly important to establish a technique for visualizing the nanoscale phase-separated structure inside SiO-GeO glass nanoparticles during the manufacturing of SiO-GeO fibers. This is because the rapidly increasing price of Ge has made it necessary to improve the Ge yield by clarifying the detailed mechanism of Ge diffusion into SiO.

Focusing of radially and azimuthally polarized beams through a uniaxial crystal.

We calculated and measured the difference between focal positions of radially and azimuthally polarized beams after passing through a uniaxial crystal. Calculations were carried out on the basis of the ray optics and the vector diffraction theory. The results of the calculations were in good agreement with those of the experiment.

Calculation of optical trapping forces on a dielectric sphere in the ray optics regime produced by a radially polarized laser beam.

We calculated the optical trapping forces on a microscopic particle in the ray optics regime for the case where a radially polarized laser beam is applied. A higher axial trapping efficiency than for a circularly polarized doughnut beam was predicted due to the large p polarization component. Three-dimensional optical trapping was expected for particles with a larger index of refraction and for objectives with a smaller numerical aperture.

Generation of a radially polarized laser beam by use of the birefringence of a c-cut Nd:YVO4 crystal.

We demonstrated the generation of a radially polarized laser beam from an extremely simple laser resonator including a c-cut Nd:YVO4 crystal as a laser medium. The oscillation in the radial polarization was based on the optical path difference between an extraordinary ray and an ordinary ray induced by the birefringence of the crystal. By simply adjusting the distance between two cavity mirrors, only the extraordinary ray became stable for the oscillation, resulting in the generation of a radially polarized beam.