Omnidirectional mirror coating design for infrared applications

An omnidirectional mirror, with a reflectance (R) of 99.5% for all angles of incidence and both polarisations, was designed from quasi-periodic dielectric stacks based on Fibonacci sequence (FS) by selecting appropriate materials for high and low refractive index layers. At R = 99.5%, the initial omnidirectional spectral range was found to be from 1437 to 1618 nm, which covers completely the telecommunications wavelength region and the S, C and L bands of the erbium doped fiber amplifier gain region. The individual layers within the FS have the same physical thickness, thus having non quarter-wave optical thickness at the centre wavelength. Optimisation from the initial design can expand the omnidirectional spectral region at R = 99.5%, as well as show a higher value of R over the initial omnidirectional spectral range. Deposition and characterisation of the mirror coating have taken place using microwave assisted direct current magnetron sputtering and various characterisation techniques.