No abstract

Polymers that are suitable for thin films are also used as materials for hybrid optical IC's; however, it is not easy in general to get a high refractive index change in the waveguide using these materials. To remove this difficulty, we have used copolymers of glycidyl methacrylic acid and methyl methacrylic acid, doped with cinnamic acid; this acid was directly photolocked, by ultraviolet exposure, to the epoxy rings of glycidyl methacrylic acid. Eventually, a refractive index change as large as 2% was achieved. Single‐mode optical waveguides with various widths were fabricated by means of the present method, and the dependence of the loss on the waveguide width and the loss in a bend were measured.

Distribution of the residual stress in InGaAs/GaAs strained layer superlattices (SLSs) has been investigated by the micro-focus photoluminescence (PL) method and PL topography. Dark lines parallel or perpendicular to [011] direction were observed in the samples by PL topography. The density of dark lines was decreased as the thickness of In0.1Ga0.9As layers increased. Such dark lines were observed even in a sample whose thickness was thinner than critical value. These dark areas corresponded to the regions where the peak wavelength of PL spectrum was shifted to longer side because of tensile stress. These results were explained well by our proposed model. That is, tensile stress acts the top of mountainous regions of wrinkles which were formed by compressive stress caused by the difference of the lattice constant between InGaAs and GaAs.

Conventional thin film optical elements consist of optical waveguides placed transversely in one plane. A new type of multilayer optical circuit element consisting of stacked thin‐film optical waveguides is proposed using polymer films in which optical waveguides are formed by ultraviolet light. After fabrication of an optical waveguide, the resistivity to solvent of the thin film increases, and hence any number of layers can be stacked without affecting the lower layers. We fabricated two‐layer and three‐layer optical directional couplers. In the former, optical waveguides are created in each layer such that they cross to each other. In the latter an additional layer is inserted between the two layers containing the waveguides. the optical coupling in these directional couplers takes place in the direction of the film thickness. the film thickness of the middle layer is measured, and the dependence of the coupling coefficient on the crossing angle and the middle layer thickness is studied experimentally. It is pointed out that an optical directional coupler with an arbitrary degree of coupling is easily fabricated. Also studied are n‐way optical equal parts dividers.