Silicon sub-wavelength grating based scalable selective higher order mode pass filter for dual-band operation

In this work, two mode pass filters (MPF) have been demonstrated using silicon sub-wavelength grating (SSWG) structures to selectively pass TE 1 and TE 2 modes for dual-band operation (O-band and C-band). These MPFs utilize waveguides embedded with nano-dimensional grating along with SWG waveguides as a novel approach to increase the mode extinction ratio (MER). Our analysis shows that the TE 1 MPF effectively blocks unwanted modes with outstanding mode rejection. At the same time, the desired TE 1 mode travels with excess losses (EL) of 2.19 dB at 1310 nm and 0.47 dB at 1550 nm. The TE 2 MPF shows similar suppression for undesired modes with ELs of 0.74 dB and 0.815 dB at 1310 nm and 1550 nm, respectively. Fabrication tolerance analysis shows that our proposed structures are tolerant within ±20 nm dimensional variation. This approach can also be applied to design dual-band mode-selective filters that deal with more than three modes, showing its scalability.