| 摘要 |
PURPOSE:To realize propagation of the single polarized wave mode surely with a simple structure, by producing the optical fiber so that the wavelength of a prescribed light source is placed in the middle between cur-off wavelengths of two polarized wave modes induced by the asymmetrical structure. CONSTITUTION:In respect to the single mode optical fiber which propagates only one polarized wave state, if core 1 is placed near the boundary of air in clad 2, it approximates the square waveguide line shown in the figure. Refractive indexes of core 1, clad 2, and the air layer are denoted as n1, n2 and n3=1. Propagation constant beta is expressed as the function of light frequency omega. In stead of the beta(omega) curve, the b(v) curve is used. Calculation is performed according to expressions I and II (a is the length of one side of the square, and lambda is the wavelength, and k0=2pi/lambda is true). In respect to the v-b<2> curve of (x) and (y) polarized waves in the minimum-degree mode for n1=1.47 and n2=1.44, curves of both polarized waves which overlap in the fiber of the symmetrical structure are separated from each other. If the wavelength is set to 1.55mum, only (x) polarized wave is propagated, and thus, the range of (a) becomes 2.80mum<a<2.90mum. |
