The optical properties of artificial two-dimensional photonic crystals containing various components are studied theoretically and using numerical modeling. The main optical characteristics, such as spectra of transmission and reflection, allowing evaluation of gain properties of a photonic crystal made of neodymium-doped glass, are studied in detail. It is shown that the threshold conditions for oscillation in the studied structures can be achieved via proper choice of their optical characteristics, which allows one to formulate the technical specifications for their manufacturing. Spectral characteristics of photonic crystals containing nanoscale silver rods embedded in a dielectric matrix are studied. Their prospective use as optical filters and polarizers is substantiated. The investigation is conducted using the method of field expansion in terms of plane waves.