BAE Systems PLC
OPTICAL FILTER

Abstract:

An optical filter 100 for a visor is described. The optical filter 100 comprises a first layer 101 comprising a first notch filter 102 arranged to attenuate electromagnetic radiation having a first wavelength .lamda..sub.1 incident normally thereupon. The optical filter 100 comprises a second layer 103 comprising a second notch filter 104 arranged to attenuate electromagnetic radiation having a second wavelength .lamda..sub.2 incident normally thereupon. The first wavelength .lamda..sub.1 and the second wavelength .lamda..sub.2 are different. The second layer 103 is stacked upon the first layer 101. In use, the first notch filter 102 attenuates the electromagnetic radiation having a predetermined wavelength .lamda. incident thereupon at a first angle of incidence .theta..sub.1 and the second notch filter attenuates the electromagnetic radiation having the predetermined wavelength .lamda. incident thereupon at a second angle of incidence .theta..sub.2, wherein the first angle of incidence .theta..sub.1 and the second angle of incidence .theta..sub.2 are different.