In this note, the optical modes established in the optical glass fibers are observed and investigated micro-photographically. These are the dielectric waveguide modes for the wave-lengths, 5,461 Å of mercury and 6,328 Å of He-Ne laser, and the fibers are considered as involving conventional waveguide phenomena treated by Maxwell's electromagnetic theory. A glass fiber of high refractive index ($n_1=1,466$) surrounded by air or glass of lower refractive index ($n_2=1,450$) is to provide a light pipe by total internal reflection. This dielectric waveguide holds optical field with propagation of light wave only in certain allowed field distributions, or modes, which satisfy Maxwell's equations and the boundary conditions.
The present experiment is concerned with circular dielectric fibers having core diameters small enough(10 μ- 20 μ) that waveguide effects are significant. The mode launching consists in imaging a point source at the entrance aperture of the waveguide and by moving the Airy disk pattern offaxis at the entrance aperture, the incidence angle beyond the critical angle is realized. Also the method of using diverging beam is employed, where the ray making the incidence angle smaller than the critical angle is automatically damped out. The mode thus obtained are $HE_{1,1}, TE_{0,1} + HE_{2,1}, EH_{1,1} + HE_{3,1}, HE_{1,2} + HE_{3,1}, EH_{2,1} + HE_{4,1}, TE_{0,2} + HE_{2,2}, EH_{1,2} + HE_{3,2}, HE_{1,3} + HE_{3,2}$. The experimental results obtained by using these methods are in complete agreement with the theoretical results obtained by the computer calculation by using the NOVA in the Korea Advanced Institute of Science.
In order to investigate image transmission on static and dynamic scanning with fiber bundle, a bundle of coated glass fibers is made. The bundle with a 10 ×5 ㎟ rectangular cross section is made up of fibers, 0.2 - 0.4mm in diameter and 55mm long. When an image of test pattern is formed upon one end aperture of fiber bundle, a transmitted image is formed at the other end. This is photographed with an optical system and a camera. In dynamical scanning, the vibration frequencies of 2Hz and 60Hz are employed. The experimental results show the dynamical scanning with closed packing of linear fibers increases the resolution of the fiber bundle.
환형 유전체 fiber와 중공형 유전체 fiber 내에서 mode가 진행할 수 있는 조건과 이들 mode의 강도분포가 이론과 실험 및 전자계산기에 의한 수치계산으로써 취급되었으며 이어서 단일 fiber 를 구성요소로 하는 fiber bundle에 의한 광학상의 전송방법과 전송된 상의 질에 관하여 이론과 실험을 통해 연구되었다. 본 논문의 이론은 Mawell 방정식에 기반을 둔 도파관 이론에서 비롯된 것이며 단색광 (Hg lamp와 He-Ne laser) 을 사용하여 mode가 fiber 내에서 진행하도록 하였다. 이렇게 해서 얻은 mode 는 전장벡터를 이용한 mode 해석방법에 의해 규정지워졌다. 사용된 fiber 의 내경은 10 μ ~ 15 μ 사이였으며 관찰된 mode는 $HE_{1,1} TE_{0,1} (또는 TM_{0,1}) + HE_{2,1}, EH_{1,1} + HE_{3,1}, HE_{1,2} + HE_{3,1}, EH_{2,1} + HE_{4,1}, TE_{0,2} (또는 TM_{0,2}) + HE_{2,2}, EH_{1,2} + HE_{3,2}, HE_{1,3} + HE_{3,2}$ 등 이었다. 다음으로 823개의 단일 fiber로 구성된 fiber bundle에 의해 여러가지 test pattern의 전송을 실험한 결과 Static Scanning 보다는 dynamical Scanning에 의해 상을 전송하는 것이 더 좋은 결과가 나옴을 알았다. 본실험에서는 dynamical Scanning으로서 주로 진폭이 3Cm, 진동수가 2Hz가 되게 하였다. 글자의 상전송을 실험한 결과 Contrast는 별로 좋진 않았으나 전송하려고 한 원래의 형태를 똑똑히 구별할 수가 있었다.
