We report numerical simulations, based on a finite difference time domain (FDTD) method, of light propagation in two-dimensional semiconductor micro optical waveguides coupled to one or several lateral stubs. The incident wave which is of transverse magnetic polarization (TM) is either antisymmetric or symmetric with respect to the middle line parallel to the waveguide. In the presence of one stub we show that the transmission spectrum contains several narrow dips provided that the boundaries of the stub are covered with a perfect metal to avoid the escape of the propagating light. The frequencies of the zeros of transmission are dependent upon the symmetry of the incident wave. This dependence can be explained by comparison with the eigenmodes of a rectangular cavity. We show that the interaction between several stubs produces a widening of the zeros of transmission into band gaps. Inserting an appropriate defect stub between a set of periodical stubs leads to a tunnelling transmission, with a narrow peak inside the gap which can be useful for selective filtering. Finally, we present a numerical calculation on a three-dimensional model which shows the ability of producing similar effects in three-dimensional waveguides.