Motoaki Furukawa

Optical characteristics of a light-focusing fiber guide and its applications

A lenslike glass fiber guide with a parabolic variation of refractive index has been developed. This optical guide named SELFOC® has the following characteristics: simultaneous transmission of laser beams modulated by wide-band signals through narrow space; optical image transmission; realization of a lens with tiny aperture or with extremely short focal length; and the possibility of being bent with a small radius of curvature without spoiling transmission characteristics. In the case of a typical fiber guide with length 1 meter and diameter 0.3 mm, transmission loss is about 0.2 dB and depolarization is about 20 dB at wavelength 0.63μ. The mode pattern of a laser beam after passing through the fiber guide is scarcely deformed. The fiber guide can be used as a transmission line or lens, in optical communication, optical data processing, and optical instruments.

New Light-Focusing Fibers Made by a Continuous Process

A new continuous manufacturing process for light-focusing glass fibers has been developed using fast ion-exchange in a special double crucible. By use of this new process, new low-loss optical fibers with a transmission loss of 20 dB/km at wavelengths between 0.81 microm and 0.85 microm and a transmission capacity of more than a few Gbit/sec for 1 km were fabricated from low-loss bulk glass prepared by an improved raw powder refinement technique and by clean melting.

Measurement of fourth-order aberration in a lens-like medium

Deformation of the spot of an off-axis Gaussian beam after passing through a lens-like glass fiber (SELFOC®) with the fourth-order aberration is investigated by using first-order perturbation theory and numerical calculation. A method for determining the coefficient of the fourth-order aberration is proposed. By this method, it is found that a SELFOC sample (0.5 mm in diameter and 150 mm in length) has a coefficient h of about 1.1, if the dielectric constant in the meridional plane of the sample is expressed as \epsilon(x) = \epsilon(0) (1 - g^{2}x^{2} + hg^{4}x^{4}) , where x is the distance from the axis of the medium and g is a positive constant.