Abstract

Periodic gratings have frequently been used for conversion of modes in highly overmoded circular waveguides [1, 2, 3]. These gratings are formed by periodically varying the waveguide radius resulting in a rippled wall structure and are usually analyzed by coupled mode theory. Very high efficiencies have been reported for these gratings but their lengths remain large compared to the waveguide transverse dimension. Various techniques have been implemented to optimize the length of these gratings [3, 4, 5], but the overall conversion length remains limited by the grating period, δ = 2π/|β_m – β_n|, where β_m and β_n are the propagation constants for the input and the output modes. The smallest conversion length reported for a TE₀₂ to TE₀₁ mode converter at 60 GHz is equal to one grating period [4]. This converter was designed for a highly overmoded waveguide with a diameter of 2.771 cm using the coupled mode equations. The efficiency reported for this converter is 97.6%.

© 1995 Optical Society of America