Kenichi Nakatate

Ultrathin image fiber with hemispherical fiber lens for medical use

The gradient-index rod lenses have been conventionally used as the objective lens of the ultrathin medical fiberscope. In this paper, we propose to apply the new hemispherical fiber lens for the ultrathin fiberscopes. The lens can be fabricated by attaching a silica rod to imagefiber and heating the free end of the rod in arc charge. As the result of our investigation, it has been known that the radius of the hemispherical lens can be controlled by the discharge time. The imagefiber with the hemispherical lens had a diameter of 0.2 mm, 1600 pixels, a working distance of 3 mm and the angle of view of 40 degrees. It has been found by evaluating its image quality that it has the sufficient feature for the practical medical usage. In addition, it has been shown that the end of the imagefiber itself can be transformed to the hemispherical objective lens, and its optical characteristics as a lens can be controlled by changing the elongating length and the preheating condition.

New method of eliminating mesh pattern of image fiber

In order to eliminate the mesh pattern due to pixels of the imagefiber, we have developed and studied the new image processing method. As a result, it has been found that the quality of the processed image is improved in brightness and contrast without blurring.

Silica-based rod lens for the medical fiberscope

The ultrathin fiberscope, in which the outer diameter is under 1.0 mm, has made possible the direct observation of narrow portions within the human body. The fiberscope mainly consists of the imagefiber, the objective lens, and the illumination fiber, and each advance of these devices has brought the reduction of the scope-diameter. We have investigated the silica based rod lens for the following merits: (1) The fiberscope can be sterilized by the (gamma) -ray instead of ethylene oxide gas which has the problem of carcinogenicity, because the silica glass has high radiation resistant characteristics. (2) The silica based rod lens can be spliced with the imagefiber without any adhesive agent by using the arc fusion splicing machine. As a result, the reliability of the fiberscope can be significantly improved. The silica based rod lens with 125 micrometers in diameter was fabricated by drawing from preform rod made by the vapor phase axial deposition method. The characteristics of their images were evaluated by the modulation transfer function method. This paper presents the details of the fabrication technique of the silica based rod lens and its characteristics.