Optical tap array using distributed-index planar microlens

The letter describes a novel optical tap array by using a two-dimensional array of planar microlenses. The present device is used to monitor a part of light which is transmitted through optical fibres. Planar microlenses to focus the light have been monolithically fabricated by the use of the electromigration technique; the focal length is 3 mm and NA is 0.15. The coupling efficiency of the initial device was 52% for coupling multimode graded-index fibres.