Evaluation of Numerical Aperture and Focusing Characteristics of Planar Microlens for Optical Interconnects

We evaluated the numerical aperture (NA) and focusing characteristics of a planar microlens (PML) for parallel optical interconnect systems. The NA of a PML of 250 mum in diameter was measured to be 0.07 using a 125 mum mask aperture to clean the beam profile. By stacking two PMLs. the NA was raised to 0.17 due to the elliptical index profile of the stacked PML. The spot diameter was 11 mum, which is nearly equal to the diffraction limit and is usable for single-mode application.