Cascaded solid-spaced filters for DWDM applications

We report in this manuscript the study of solid-spaced Fabry-Perot filters. The use of high quality wafers as thick spacers and broadband dielectric mirrors with only few layers provides filters which have almost the same specifications as classical WDM interference filters. Multiple cavity filters, composed of single cavities of equal or different thick spacers are easy to manufacture and exhibit very low absorption and scattering losses. Experimental results concerning simple and double cavity filters with thick spacers centered at 1.56 μm with a maximum transmission more than 98 % and a full-width at half-maximum (FWHM) of about 0.5 μm are exposed. We then propose different solutions for the extension to triple cavity filters with improved spectral properties.