On-chip dual-band higher order mode pass filter using silicon subwavelength grating

Abstract

In mode division multiplexing (MDM) technology multi-band higher order mode (HOM) pass filters are rarely introduced. However, these filters will support the MDM technology to be universal for all available wavelength bands used in fiber optic communication systems. In this work, two TE1 mode pass filters (MF1 and MF2) have been proposed using silicon subwavelength grating (SSWG) structures embedded in the multi-mode waveguide to operate in a dual band (O-band and C-band). The MF1 with gratings of two distinct grating periods and a device length of only 23 μm shows excellent performance in terms of excess losses (EL) of 0.20 dB and 0.38 dB at the center wavelengths of the O band and C band respectively, with TE1-TE0 extinction ratios (ER) of 56.54 dB and 47.73 dB at the respective wavelengths. The TE0 mode rejections are < -25 dB in the O-band and < -45 dB in the C-band. On the other hand, the MF2 designed with gratings of uniform grating period has an ultra-compact device length of only 18 μm and shows almost similar mode rejections for TE0 mode as MF1. The ELs are 0.95 dB and 0.374 dB at the center wavelengths of O-band and C-band respectively, while the TE1-TE0 ERs are 40.60 dB and 61.36 dB at these respective wavelengths. Both of the filters have bidirectional properties. Fabrication tolerance analysis indicates that our proposed devices are tolerant within ±20 nm variations in the period, pitch, and width of the gratings.