This paper presents the design concepts of small size of 1×8 silicon-based arrayed waveguide grating (AWG) de-multiplexer in order to improve its optical properties such as insertion loss and crosstalk. First, Transmission Star Couplers (TSC) is added into Free Propagation Region 1 (FPR1) which has refractive index 1.455. It is found that, the appropriate value of refractive index of TSC area is 1.460. After that, the width of the waveguide in an arrayed waveguide is increased from 6 μm to 8 μm. Here, the insertion loss of AWG is decreased from 1.79 dB to 1.52 dB, while the crosstalk is increased from -23.94 dB to -21.84dB. To maintain the increased crosstalk problem, the traditional output waveguide structure is then replaced by a taper structure which has start width 10 μm and end width 6 μm. As a result, the insertion loss is reduced from 1.52 dB to 1.06 dB, and the crosstalk is reduced from -21.84 dB to -24.13 dB. Furthermore, some part of output waveguides with refractive index 1.460 are overlapped with Free Propagation Region 2 (FPR2) which has refractive index 1.455. The proper length of overlapping regions is 155.2 μm. By using all design concepts, the insertion loss and crosstalk of the proposed AWG are 0.11 dB and -26.80 dB, respectively. Therefore, the appropriate structure of proposed AWG can be achieved. In addition, the size of the proposed AWG is the half of that of the traditional AWG, and its insertion loss is lower than that of the traditional AWG which its insertion loss is 1.26 dB. © 2013 Praise Worthy Prize S.r.l. - All rights reserved.