Radiation Patterns From Parallel, Optical Waveguide Directional Couplers - Parameter Measurements

Parallel coupled waveguides are the basic building block for a number of integrated optical devices; these include switches,1-6 modulators, and channel dropping or adding filters.7 The techniques used to measure coupling parameters are often visual in nature. The simplest approach is to observe the energy exchanges between the parallel guides from the surface scattering of these guides viewed through a microscope. However, this is not always feasible; e.g., operation at longer wavelengths away from the visible, with low-loss surface scattering guides, and in cases where the energy at the surface is rather low, as it happens with Ti diffused guides in LiNb(>3. In such cases, the technique developed by Ostrowsky et al.8 is quite useful. They observed the fluorescence from RhB-doped polyurethane film over the strip guides pumped by an argon laser. In this paper, we present a method found useful in measuring the parameters of such couplers. Basically, the method consists of observation of the interaction length dependence of the coupling via radiation pattern measurements;9 the radiation patterns are obtained by moving an output coupling prism along the coupled waveguide region. 2685