An asymmetric optical interleaver (AOI) based on G-T etalon type is proposed. In principle, by adjusting two waveplate parameters and the etalon reflectance, asymmetric interleavers with any spectral bandwidth ratio can be constructed. Simulation on the output of asymmetric optical interleavers with spectral bandwidth ratio of 1∶3 and 1∶7 are presented. The analysis on how to determine the parameters of the two waveplates, the reflectance of the Gires-Tournois etalon and their matching are given. A device with spectral bandwidth ratio of 1∶3 and 1∶7 is designed and fabricated, the output of 1∶3 device is 0.38 nm and 1.15 nm at 3 dB and the output of 1∶7 device is 0.191 nm and 1.331 nm at 3 dB. Experimental results (spectral bandwidth ratio) are in good agreement with the design.