Novel High-Isolation Polarization and Multimode Division Circuit for Circular Waveguide

Modern optical fibers are capable of transmitting multiple wavelengths simultaneously using the wavelength division multiplexing (WDM) method for multiple-input multiple-output (MIMO) communication systems. They have been put to practical use by increasing the communication speed. This letter proposes a new WDM circuit that transmits and separates the TE
_11x
, TE
_11y
, and TM
₀₁
modes (polarization and multimodes) within a circular waveguide in the 5.6-GHz band. The transmission loss of each mode/polarization is up to 1.1 dB, and the isolation between modes/polarizations is more than 28.7 dB in a 200-mm-long circular waveguide. As a result, the independence of each mode and polarization applicable to MIMO communication systems is verified.