Optimised design of even-order optical low-pass and high-pass multilayer filters by method of coefficient matching

An algorithm is developed to design optimised lowpass multilayer filters by equating the coefficients of the multilayer transmittance with those of the Chebychev transmittance. Results are obtained for a 17th-order, lowpass multilayer show that it has optimised Chebychev-like performance in the passband. Its transmittance characteristic falls short of optimum performance in that the ripples at low frequencies are less than the specified value. Nonetheless, its performance compares favourably with other well-established methods of design. By contrast, a high-pass multilayer, designed using the same approach, has a performance which falls short of the accepted norm. Evidence leads us to conclude that coefficient matching with Chebychev polynomial is more suited to the design of lowpass multilayers than highpass multilayers.