Insertion losses in micromachined free-space optical cross-connects due to fiber misalignments

One of the most promising applications of MOEMS in Optical Networks is represented by free-space electro-mechanical Optical Cross-Connects (OXCs); these components show lower attenuation and lower insertion losses than concurrent components based on waveguides. Although some commercial micromachined electro-mechanical OXCs have been recently announced in the market, further deployment of these devices will certainly require decreasing insertion losses by proper design techniques of both, the electromechanical devices and the system packaging. In this document, we study insertion losses in micromachined free-space OXCs and the related packaging challenges; we assume in our discussions Single Mode Fiber (SMF) Cross-Connects using mirrors as beam steering devices. We start with an introduction to micromachined OXCs architectures, actuation mechanisms and collimators. In section 2, we present a study of insertion losses in SMFs links; the coupled effect of lateral and angular fiber misalignments is discussed. In section 3, we discuss insertion losses in OXCs when quarter-pitch GRIN lenses are used as fiber collimators; both sections 2 and 3 are based on Gaussian beam optics. In section 4, we explore the application of Scalar Diffraction Theory to OXC design, this is for calculating insertion losses including diffraction at the mirror plane. Finally, conclusions on insertion losses and the required fiber positioning accuracy are given.