Simple optical wavelength-division multiplexer component that uses the lateral focusing scheme of a planar microlens

A planar microlens beam guide that is based on the lateral focusing property of gradient-index planar microlenses is realized for a wavelength-division multiplexer (WDM) component without precision alignment. By stacking two planar microlenses, we obtain a nearly circular focused spot of ~5-µm diameter by lateral focusing, which is comparable with that of a single-mode fibers. A fabricated WDM component that consists of four stacked lenses and microfilters inserted into the slits made in a substrate is demonstrated. The port-to-port coupling loss is 3-5 dB, and an extinction ratio of larger than 20 dB for multiplexed-demultiplexed wavelengths of 780 and 633 nm, respectively, is achieved.