A four-channel integrated optical wavelength de-multiplexer is experimentally illustrated on a silicon-on-insulator (SOI) substrate.With the aid of cascaded micro-ring resonators,the whole performance of the wavelength demultiplexer is improved,such as 3 dB bandwidth and channel crosstalk.Based on the transform matrix theory,a four-channel wavelength de-multiplexer with average channel spacing 4.5± 0.5 nm (3 dB bandwidth ～ 2 ± 0.5 nm)is demonstrated at telecommunication bands.For each channel,the extinction at the adjacent channel is below -39dB and the out-of-band rejection ratio is up to 40dB.The channel dropping loss is below 5dB in the five FSR spectral response periods (near 100 nm).