We report the results of study of upconverted emission in the band 520 to 600 nm from waveguides made of poly(methyl methacrylate) (PMMA) doped with laser dye 4- (Dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)4H-pyran known as DCM. The emission could be excited using CW laser pumping within the range 630 nm to 800 nm with intensity below 1 kW/cm<SUP>2</SUP>. The excitation mechanism, instead of the two- photon absorption, more likely involves exciton-like localized states below the S1 singlet state. These localized states, being excited by low energy photons can assist in populating upper singlet states according to the scheme of the excited state absorption. We also pay special attention to material photobleaching that accompanies upconverted emission. This effect leads to refractive index decrease at the wavelength of the pump. Computer simulations based on numerical solutions of nonlinear propagation equation as well as experiments show that photobleaching leads to irreversible branching of optical pump beam that propagates through a dye-doped polymer waveguide.
We report on single optical beam splitting into several beams (the optical branching effect) in a single mode slab waveguide
made from poly(methyl methacrylate) (PMMA) doped with dye 4-(Dicyanomethylene)-2-methyl-6-(pdimethylaminostyryl)
4H-pyran known as DCM. The effect is associated with permanent refractive index decrease accompanying upconverted dye photobleaching. Unlike the defocusing Kerr effect, the refractive index response to the optical field is nonlocal in time for the index depends on the absorbed energy instead ofthe instant light intensity. The effect therefore takes place at much lower power then nonlinear propagation effects in Kerr media (less than 1 kW/cm2 ).The
proposed model of branching uses soliton-like solutions of Shrodinger-type nolmear propagation equation complemented by the rate equation for the refractive index change. Computer simulations based on the model demonstrate all the effects observed experimentally such as beam splitting into two primary side branches followed by their collapse into multiple secondary branches.
We present the results on fabrication of plastic integrated optical elements using molding, liquid jet delineation, and UV irradiation. Coupling gratings with a period of 620 mm<SUP>-1</SUP> and a diffraction efficiency of 3.3 percent were molded in a preheated poly(methyl methacrylate) planar waveguide using master saw shaped grating. An experimental device is also described which uses computer controlled micro syringe to dispense polymer solution onto a moving substrate. This device consumes thousand times less material to produce integrated optical circuits than equivalent spin- casting equipment.We have made various structures such as Y- branches and Mach-Zehnder interferometers. All the structures demonstrated good performance. The same device was also equipped with a microscope-type UV illuminator for noncontact delineation of optical structures in polyimide films. The operation is based on the refractive index increase due to photo-oxidative decomposition of the material. The index difference 0.02 between exposed and unexposed regions is sufficient to define light guiding channels in polyimide without using liquid developing. UV radiation was also used to make graded-index polyimide waveguides. Their refractive index profile was successfully reconstructed by a specially developed calculation technique. All the techniques combined together give us the cost efficient tool for the fabrication of plastic integrated optics.