In this paper, we present the improvement of optical properties of lx8 arrayed waveguide grating (A WG) de multiplexer by adding Transmission Star Couplers (TSC) 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. Using this method, the insertion loss of A WG decreased from 1.79 dB to 1.58 dB while the crosstalk increased from -23.94 dB to -22.49 dB. To maintain the problem of the increased crosstalk, the traditional output guide structure is replaced by a taper structure which has start width 11 /lm and end width 6 /lm. Then, the insertion loss is reduced from 1.58 dB to 1.09 dB, and the crosstalk is reduced from -22.49 dB to -24.94 dB, respectively. Therefore, by using all design concepts, the appropriate structure of proposed A WG can be achieved. The size of the proposed A WG is the half of that of the traditional A WG, and the insertion loss of the proposed A WG is lower than that of the traditional A WG.

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