Photonic bandpass filter characteristics of multimode SOI waveguides integrated with submicron gratings

It has been shown that a fundamental mode adiabatically launched into a multimode SOI waveguide with submicron grating offers well-defined flat-top bandpass filter characteristics in transmission. The transmitted spectral bandwidth is controlled by adjusting both waveguide and grating design parameters. The bandwidth is further narrowed down by cascading two gratings with detuned parameters. A semi-analytical model is used to analyze the filter characteristics (1500 nm <= lambda <= 1650 nm) of the device operating in transverse-electric polarization. The proposed devices were fabricated with an optimized set of design parameters in a SOI substrate with a device layer thickness of 250 nm. The pass bandwidth of waveguide devices integrated with single-stage gratings are measured to be similar to 24 nm, whereas the device with two cascaded gratings with slightly detuned periods (Delta Lambda = 2 nm) exhibits a pass bandwidth down to similar to 10 nm. (c) 2018 Optical Society of America