Ultra-compact and Ultra-broadband Mode Exchangers for Transverse Magnetic Modes using Subwavelength Grating Structures

In this work, we have proposed two ultra-compact and ultra-broadband transverse magnetic (TM) mode exchangers (MEXs) (TM0 ↔ TM1 and TM0 ↔TM2) using subwavelength grating (SWG) structures. Our simulation results indicate exceptionally high conversion efficiency across a 400 nm bandwidth, spanning the O+C+L bands. We evaluated the performance of these devices in three distinct bands: O-band, C-band, and L-band. The TM0 ↔ TM1 MEX operating as a TM0 to TM1 mode converter exhibited peak efficiencies of 92.58, 94.76, and 94.69% in these bands, respectively. Likewise, the TM0 ↔ TM2 MEX operating in TM0-to-TM2 mode conversion demonstrated similarly high efficiency across the entire range, with peak efficiencies of 89.7, 97.55, and 97.55% in the respective bands. We optimized the footprint of both devices, achieving the lowest footprint for the TM0 ↔ TM1 MEX of 4.30 × 1.40 µm and for the TM0 ↔ TM2 MEX of 4.90 × 1.87 µm. Moreover, our proposed devices exhibit very low crosstalk (< –10 dB for TM modes and < –45 dB for transverse electric (TE) modes) and are fabrication-tolerant within ±20 nm.