Square top BPF(band pass filter) with wide passband and square shaped top is designed and fabricated. The multilayer systems are much complicated so that intuitive understanding is generally inhibited. Therefore new method of analysis is developed and introduced in this study. Considering two effective surfaces in multilayer system, it is possible to analyze a single peak BPF which has two high reflectance multilayer stacks and a single spacer between them. The method can equally be used in designing a single peak BPF and then repeating single peak BPF designing process properly, it arrives finally to the square top BPF wanted. Under the condition that total number of layers does not exceed 20, reasonable stability against random thickness error within 4%, typical square top BPF design is obtained for various halfwidth.
For the most precise thin film thickness monitering, the white light thickness monitoring system using a monochromator and a lock-in amplifier is developed in this experiment. Lock-in amplifier is also developed for noise reduction in the white light thickness monitoring system.
Square top BPF prepared by thermal vacuum evaporation has 5∼10% lower peak transmittance and halfwidth deviation below ±5% compared to the design value. And its center wavelength of transmittance is shifted within ±1% from its reference wavelength.
