Theoretical analysis of free-space optical coupling loss in a multileveloptical system

摘要

An approximate analytical solution involving the evaluation of the overlap integral method has been developed toestimate the coupled optical power in a multilevel optical system. The transmitter and receiver optics are located ondifferent planes, vertically separated by a distance Z. 45° micro-mirror pairs are used to facilitate out-of-plane reflectionof the optical beam in order for the transmitter and receiver components to be optically linked. The optical componentsconsist of planar waveguide focusing elements, involving a combination of graded-index effect and lens front curvature.Optical signal in many active and passive optical devices can be well approximated by a Gaussian beam. The couplingloss formulas have been derived to support elliptical and circular Gaussian beam analysis. Spot size mismatch, non-idealpropagation distance, axial offset, mirror angular deviation and relative tilt between the two planes are majorcontributors toward optical power loss in a multilevel optical system. The derived coupling loss formulas has beenapplied to find the optimal coupling condition like micro-mirror positions, Z, relative distances of optical elements fromthe micro-mirror, beam spot size, etc. for a prototype system. BPM simulation results are in good agreement with thenumerical results obtained by the approximate analytical solutions. The derived coupling km formulas can be used toestimate optimal optical power loss in a single level or multilevel optical system in MOEMS based optical circuits aswell as in a conventional optical system where paraxial approximation is assumed.