Abstract—in this paper we modified a simple two-dimensional photonic crystal waveguide by creating micro cavity resonators in order to increase the output light emission which can be applicable to photonic integrated circuits. The micro cavity resonators are constructed by removing two tubes close to the waveguide output. Coupling emitted light from waveguide with those micro cavities, results increasing intensity of waveguide output light. Inserting a tube in last row of waveguide, we have improved directionality of output light beam. Keywords—photonic crystal, waveguide, micro cavity resonators, directional emission I. INTRODUCTION HOTONIC crystal (PC) has the potential to be a fundamental of future optical integrated circuits. Recently, a variety of devices such as a low loss waveguide circuit fibers, couplers and multiplexers are demonstrated on membranes of 2D PC [1]-[2], to make all optical systems. Coupling efficiency is an important subject to use the PC- based devices [3]. Coupling efficiency between PC waveguide and external optical components is low, because of difference in their refractive index and mode size [3] and diffracting the light emerging from the PC, in all directions [4]. To overcome the poor coupling efficiency of PCs, many investigations such as coupling via out-of-plane gratings, combinations of ridge waveguides and tapers, or evanescent coupling [5], micro cavity-to-waveguide side coupling system with a reflector at one end of the waveguide for the feedback [6] have been reported. But, applying these solutions to a compound semiconductor based with air cladding is very difficult [3]. In this paper we studied photonic crystals containing defects which have the ability to capture a particular light frequency around those defects. The distinct advantage of our proposed structure is the lack of any complexity, which contains only absence of a few rods, close to the end of the waveguide. In addition, no A. Mobini is with Electrical Engineering Department, Shahed University, Tehran 3319118651, Iran; (e-mail: mobini@shahed.ac.ir). K. Saghafi is with Electrical Engineering Department, Shahed University, Tehran 3319118651, Iran; (corresponding author phone: +98-21-55228813; fax: +98-21-55228814; e-mail: saghafi@shahed.ac.ir). V. Ahmadi is with the Department of Electrical Engineering, Tarbiat Modares University, Tehran, Iran, and also with Laser Research Center, Tehran 11368-8486, Iran (e-mail: v_ahmadi@modares.ac.ir). modifications are made to the rods’ radii and also there is no change in the crystal lattice constant. II. PROPOSED STRUCTURE We considered a two dimensional slab PC with dielectric rod in air background. The lattice is square with r/a=0.2 with TE polarization. We calculated the dispersion diagram by means of PWE (plane wave equation). The band gap region extends from 2.267<λ/a<3.096 [7]. The simple waveguide is constructed by removing one column mediate tubes from photonic crystal slab. The input source is an adequately broadband Gaussian pulse with a frequency center at λ/a=2.503. This structure has spherical output beam intensity profile and the waveguide outlet behaves like a single source point that emits in air. Two defects interned in regions close to the end of waveguide surface in (a,-a), (-a,-a) coordinate in x-z plan, as shown in Fig.1, that each one can act as a micro cavity resonator and drop distinct wavelength from input light. Fig. 2 shows the yield figure of each cavity. Fig.1 Schematic drawing of the square-lattice PC waveguide with 2 local micro cavity resonators at (a,-a) and (-a,-a) coordinate in x-z plan III. RESULTS AND DISCUSSION We have calculated the output intensity with respect to λ/a in different value of x axis at distance z=15a from PC surface, that shown in Fig. 3. The transmitted intensity has a maximum in λ/a =2.503 with transmission coefficient of 88%. In fact in this wavelength the cavities behave such as two point sources and the emitted waves interfere with transmitted wave from waveguide. The steady-state field profile evolution of the PC Increasing Directional Intensity of Output Light Beam from Photonic Crystal Slab Outlet Including Micro Cavity Resonators A. Mobini, K. Saghafi, and V. Ahmadi P World Academy of Science, Engineering and Technology 58 2009 275