Simple structural quasi-optical circulator composed of tapering and bending waveguides

An optical circulator function has been realized without using any magnetoo ptic effect by placing a multimode tapered bending waveguide made of passiv e material in rotational symmetry. The higher-order propagating mode compon ents selectively radiate from a bend of a certain curvature, and the lower- order mode components pass through the bend and radiate from the tip of the taper. When the lower-order modes are launched into the waveguide, light r adiates from the tip, and couples to the propagating higher-order modes of the next waveguide at its bending section. This phenomenon is accompanied b y a change in the transmission mode distribution and an excess loss of at l east 3 dB. However, if the evaluation is only by the transmitted power, the device exhibits the circulator function. This small and low-cost optical d evice is effective in a low-speed and short-distance bidirectional data com munication system. In this paper, in order to confirm the basic principles, microwave simulation was carried out to examine in detail the radiation ch aracteristics from the tapered bending waveguide with a resolution of one w avelength. An extinction ratio of more than 18 dB was realized when the dis tance between the adjoining waveguides was about one wavelength. (C) 2000 S cripta Technica.