Narrowband optical thin-film filters with distributed cavity modes

This paper presents a narrowband optical thin-film filter based on a multiple-layer stack with layer thicknesses varying in the direction of light propagation (termed as chirping). By chirping, we distribute the cavity of a Fabry–Perot resonator over several periods, causing a wider spatial distribution of the electric field of the resonant modes. Better control of the mode distribution may improve the performance of VCSEL devices. These chirped filters are investigated by theoretical model calculations with respect to important optical design parameters such as chirp functions, chirp distribution, chirp volume, total number of periods and the refractive index contrast. Additionally, the chirped filters are fabricated and their optical characterization results are compared with the numerical investigations.