Simulation and Analysis of Transmission Characteristics for the Flat-Top Thin Film Filter

In this paper, the vertical multi-cavity film stack is divided into system A and B by using Smith method, and each part is composed of coating unit including reflection layers, cavity layers and coupling layers. By changing the coating unit parameters, the reflective variations of system A and B are obtained after coating units parameters are changed in two-cavity F-P structure. By changing the intersections of the reflectivity curves and the zero points of the half-phase sine value, the causes of flat top response characteristic are analyzed. The factors which impact the performance of flat-top thin film filter are obtained. At last, a three half film structure is designed which has the good performance. Its 0. 5 dB bandwidths is 0. 52 nm, 3 dB bandwidth is 0. 67 nm, and 25 dB bandwidth is 1. 59 nm, the rectangular factor is 2. 37.