In this paper, a three dimensional analysis of an ultra-compact sharp trench waveguide bend structure modified with small local photonic crystals is presented. The structure used here is based on a previous proposal . To fully investigate the behavior of the structure, especially mode coupling and off plane radiation losses – (that are ignored in two dimensional calculations ) as well as the limitations caused by the effective index approximation in the two-dimensional (2D) simulations, we simulated realistic three dimensional structures using the finite integration technique. Furthermore, a structure on an InP substrate is compared with a Si/SiO2 based structure in order to check the influence of vertical index contrast on the device performance. One of the structures based on InP substrate was then fabricated and characterized to validate our conceptual predictions.