Optomechanical design of tunable InP-based Fabry-Perot filters for wavelength division multiplexing applications

摘要

Micro-machined tunable Fabry-Perot interferometers based on compound semiconductors have earlier been proposed for fiber optic communications employing wavelength division multiplexing (WDM) for wavelengths around 1.55 μm. The cavity length in micromachined interferometers is varied by displacing one of the two distributed Bragg reflector (DBR) mirrors by electrostatic actuation of supporting beams. The filter's optical response for varying cavity lengths is simulated by a transfer matrix method, and the optical tuning efficiency of the filter is 0.53. We investigate three conventional filter designs using the finite element method (FEM) and compare it with a new proposed filter design. Using a mathematical model, deflection is analytically calculated and compared with finite element analysis results. Due to the way in which the mirror is integrated with a suspending framework of beams, bending within the mirror during actuation cannot be averted. The filter's optical performance demands that the mirror remain so flat that the maximum bending deflection is 1 nm for the mirror of given dimensions, Using a criterion based on mechanical and optical considerations, the dimensions of the beams suspending the mirror are optimized for each filter design under investigation. Combining the optical and mechanical simulations by FEM, wavelength tuning characteristics for each filter design are determined.