Polarization-selective Coupler Research Articles

Design Methodologies of Compact Orthomode Transducers Based on Mechanism of Polarization Selectivity

An orthomode transducer (OMT) design is presented and implemented for future RF and millimeter-wave applications. The novelty of the proposed OMT stems from a distinct concept of handling dual-polarized signals on the basis of a polarization-selective coupler (PSC). The theory of the PSC is developed and understood through analyzing its constituent waveguides. Such waveguides are hybrid forms of nonradiative dielectric waveguide and substrate-integrated waveguide. An equivalent circuit model is deduced for modeling dispersion characteristics of the PSC. Consequently, design methodologies supported with comprehensive theoretical study and simulation analysis for a PSC-based OMT are developed and examined. The general design of a PSC-based OMT basically depends on a dielectric slab coupler waveguide with a longitudinal periodic PEC polarizer wall in its middle. Practical limitations for this design is discussed and supported with solutions using a proposed top slot coupler instead of the dielectric slab coupler. Closed-form equations are obtained as design recipes for computing structure dimensions and bandwidth based on operating frequency and the material parameters. The proposed structure is prototyped and measured. Measured results show an acceptable agreement with simulation results.

Anisotropic polarization maintaining optical fiber ring resonators

Suppression of the polarization drift of optical fiber ring resonators is investigated both theoretically and experimentally by employing anisotropy in a polarization maintaining fiber ring. A general analytic expression for the transmission of the device is derived allowing the fiber modes to exhibit any combination of polarization crosstalk, differential loss or differential coupling. The analysis shows that a moderate level of ring anisotropy, such as that of 10 dB in line polarizer or polarization selective coupler, is sufficient to greatly suppress the drift of the eigenstates of polarization (ESOPs), finesse and resonant point, restoring the device's suitability for most practical applications. An inevitable consequence of introducing ring anisotropy is the loss of orthogonality of the ESOPs. This effect limits the anticipated benefit in high sensitivity applications. A practical anisotropic PMRR is demonstrated by inserting a thin film of nematic liquid crystal between the two halves of the polished coupler of the ring. This resonator demonstrates a polarization response immune to environmental perturbations.