Optical filter and method for linearization of optical power equalizer

In a combination comprising an optical power equalizer and an optical filter, an output of said optical power equalizer across a wavelength band exhibiting a deviation from linearity correctable by an ideal quadratic-shaped insertion loss curve centered about a central wavelength of the wavelength band, the optical filter being arranged in series with the optical power equalizer for correcting the deviation from linearity, said optical filter comprising:

• a first layer formed of a first material and having a first layer thickness according to the formula
• first layer thickness=mλ/(4nfirst),
• where m is an odd multiple integer, λ is a center wavelength of the wavelength band, and nfirst is the refractive index of the first layer;
• and
• a second layer formed of a second material and having a second layer thickness according to the formula
• second layer thickness=λ/(4nsecond),
• where λ is the center wavelength of the wavelength band, and nsecond is the refractive index of the second layer, wherein said optical filter exhibits an insertion loss curve approximating the ideal quadratic-shaped insertion loss curve in the wavelength band and has a maximum insertion loss at the center wavelength of the wavelength band, and wherein said refractive index of said second layer is variable and the insertion loss at said center wavelength is dependent on said refractive index of said second layer.