CROSS-SHAPED BANDPASS-FILTERS FOR THE NEAR-INFRARED AND MIDINFRARED WAVELENGTH REGIONS

A photolithographic process has been used to form cross-shaped pattern s in 3-mu m-thick nickel foils. Patterns with cross arm dimensions in the 10-20-mu m range, and with periodicities in the 16-26-mu m range, yield self-resonant bandpass filters for wavelengths in the 20-25-mu m region. Transmittances as high as 80% were achieved with center wavel ength-to-bandwidth ratios (lambda(R)/Delta lambda) of similar to 5. We present a simple empirical formula that relates the wavelength of pea k transmittance, or resonant frequency, with cross dimensions and peri odicity. (C) 1996 Optical Society of America