Compact Third and Fourth Order Mode Pass Filters Based on Backward Mode Conversion Gratings of Sub-wavelength Dimension

Mode filter has great significance for a successful and smooth transmission in a mode division multiplexing (MDM) system. It can reduce modal crosstalk (XT) and enhance the system performance in MDM technologies. In order to achieve high transmission capacity in MDM, here we have proposed a unique concept of designing compact higher order mode pass filter (MPF) based on backward mode conversion gratings of sub-wavelength dimension in the 2 μm band. Our proposed method is highly scalable for realizing MPF of any order which can efficiently filter multiple modes simultaneously. Using this approach we have designed two MPFs to pass higher order transverse electric (TE) modes. The simulated results show excellent performance for the TE<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> MPF in term of low excess losses (EL) (<1.01 dB) and insignificant XTs from undesired modes. For the TE<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf> MPF, the ELs < 0.98 dB in the entire operating band with insignificant XTs.