The transmissive Gires-Tournois etalon (GTE) is proposed based on composite couplers. By combining such GTEs with Mach-Zehnder interferometer (MZI),we obtain a new interleaver. The output expression is derived and numerical simulation is performed. The simulation indicates that it has good passband flatness (flat-top),large isolation,wide passband and stopband bandwidths. By optimizing the spectrum it shows that when the sum of cavities of GTEs is fixed,the larger the passband bandwidth gets,the smaller the isolation will be,i.e.,isolation and bandwidth are incompatible. However,this contradiction can be overcome by increasing the sum of cavities,i.e.,interleaver′s spectral performance can be enhanced by increasing cavities. Compared with the ring resonator assisted interleaver,the proposed interleaver can achieve rectangle spectrum without using the phase shifter and its spectrum is uniform in the whole wavelength band. Further more,a set of cascaded ring resonators is proposed as the dispersion compenastor to overcome the dispersion of the interleaver. Dispersion compensation ability is very good and can be enhanced by increasing the number of ring resonators.