Optical to microwave conversion in a traveling wave electro-optic polymer based device

This paper describes the design of an optical to microwave converter. The physical effect used for the conversion is based on the non-linear behavior of an electro-optic polymer material. The microwave frequency is generated by the way of an optical waves mixing process, which means by the frequency difference of two optical waves propagating simultaneously inside an optical waveguide. If one of these optical waves is modulated by an informative signal, the microwave signal will infer the modulation. The converter is designed for working at the 1.55 μm optical telecommunication wavelength. The active waveguide is built with the crosslinked PMMA-DR1 electro-optic copolymer, and the cladding layers are made of NOA material. For the first characterizations there is no need of a master-slave configuration for the sources, and the two optical waves are produced by highly stable and fine tunable lasers. The microwave signal is collected on a strip line which characteristic impedance has to be adapted to the conversion process. Simulations have been conducted showing the feasibility of the method and by matching the velocities of the microwave signal and of the optical signal it is possible to create constructive microwave photonic mixing at more than 60 GHz. To achieve the conversion it is necessary to work with a traveling-wave configuration. Some special test devices have been built for the determination of the NOA material permittivity leading to a precise adjustment of the effective index of both optical and microwave waveguide. From all these measurements it has been possible to design completely the device, which is now under test.