A method and system for constructing at least one intermediate frame of an image between first and second frames in a system such as a wired or wireless telephone network. The parts are formed of an alloy that, besides of at least 20 weight % chromium, consists of iron and one or several additional alloy portions that in sum do not amount to more than 10 weight %. The trench has surface orientations including a surface orientation of a sidewall at an upper stage made slower in epitaxial growth speed than a surface orientation of a sidewall at a lower stage. The method extends the application range of constant-length delay line PMD compensators while reducing the cost of implementing high-performance PMD compensation. An adaptive filter is then used if the SNR of the output of the averaging filter reaches a threshold.