Transmissive and reflective type multi-nanolayer electro-optical modulators for chip-to-chip free space optical interconnection: wavelength-scale electromagnetic modelling by the method of single expression

Modulating characteristics of transmissive and reflective Fabry–Perot type multi-nanolayer conductor–dielectric electro-optical modulators (EOMs) for chip-to-chip free space optical interconnection are analyzed via wavelength-scale electromagnetic modelling. For electromagnetic analysis the frequency-domain method of single expression is used. The considered EOM structures consist of an electro-optical spacer of LiNbO₃ covered by two thin ITO conducting nano-layers, surrounded by Si/SiO₂ distributed Bragg reflectors (DBRs). In the case of transmissive EOM the DBRs are symmetric regarding the spacer, while in the case of reflective EOM they are asymmetric to provide high reflectance for the structure. From four possible types of DBRs the suitable structure has been chosen with layers of higher permittivity adjoining to the ITO nano-layers. ITO nano-layers serving as electric contacts for supplying modulating electrical signal to the electro-optical spacer are parts of the multi-nanolayer structures and are included in the electromagnetic models. An incident radiation from an external laser diode at 1.55 μm wavelength is considered. The optimal configurations of the EOM structures providing a high peak in the transmittance for the transmissive EOM and a narrow dip in the reflectance for the reflective EOM are proposed. Efficiency of optical wave intensity modulation is analyzed by means of influence of electro-optical spacer’s permittivity change on the transmittance and the reflectance of the EOM structures.