Abstract: A two-cavity Fabry-Perot(F-P) structure is compared to the conventional F-P structure. The characteristics of transmission spectra for the conventional and the two-cavity F-P structures are theoretically analyzed. Based on the theoretical analysis, the transmission spectra of conventional, symmetric and asymmetric two-cavity F-P structures are simulated, and the results are discussed. The results show that, while the increase of the cavity length of a conventional F-P structure results in multiple resonant peaks on both sides of the main peak, the two-cavity F-P structures of the same total length can improve spectral range effectively and keep the main peak without degrading the performance through proper design of the mirror reflectivity and cavity lengths. The mirror reflectivity also